Cite as: 572 U. S. ____ (2014)

Opinion of the Court

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SUPREME COURT OF THE UNITED STATES

No. 12–158

CAROL ANNE BOND, PETITIONER

v.

UNITED STATES

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF

APPEALS FOR THE THIRD CIRCUIT

[June 2, 2014]

CHIEF JUSTICE ROBERTS delivered the opinion of the Court. [Complete.]

The horrors of chemical warfare were vividly captured by John Singer Sargent in his 1919 painting Gassed. The nearly life-sized work depicts two lines of soldiers, blinded by mustard gas, clinging single file to orderlies guiding them to an improvised aid station. There they would receive little treatment and no relief; many suffered for weeks only to have the gas claim their lives. The soldiers were shown staggering through piles of comrades too seriously burned to even join the procession.

The painting reflects the devastation that Sargent witnessed in the aftermath of the Second Battle of Arras during World War I. That battle and others like it led to an overwhelming consensus in the international community that toxic chemicals should never again be used as weapons against human beings. Today that objective is reflected in the international Convention on Chemical Weapons, which has been ratified or acceded to by 190 countries. The United States, pursuant to the Federal Government’s constitutionally enumerated power to make treaties, ratified the treaty in 1997. To fulfill the United States’ obligations under the Convention, Congress enacted the Chemical Weapons Convention Implementation Act of 1998. The Act makes it a federal crime for a person to use or possess any chemical weapon, and it punishes violators with severe penalties. It is a statute that, like the Convention it implements, deals with crimes of deadly seriousness.

The question presented by this case is whether the Implementation Act also reaches a purely local crime: an amateur attempt by a jilted wife to injure her husband’s lover, which ended up causing only a minor thumb burn readily treated by rinsing with water. Because our constitutional structure leaves local criminal activity primarily to the States, we have generally declined to read federal law as intruding on that responsibility, unless Congress has clearly indicated that the law should have such reach. The Chemical Weapons Convention Implementation Act contains no such clear indication, and we accordingly conclude that it does not cover the unremarkable local offense at issue here.

I

A

In 1997, the President of the United States, upon the advice and consent of the Senate, ratified the Convention on the Prohibition of the Development, Production, Stockpiling, and Use of Chemical Weapons and on Their Destruction. S. Treaty Doc. No. 103–21, 1974 U. N. T. S. 317. The nations that ratified the Convention (State Parties) had bold aspirations for it: “general and complete disarmament under strict and effective international control, including the prohibition and elimination of all types of weapons of mass destruction.” Convention Preamble, ibid. This purpose traces its origin to World War I, when “[o]ver a million casualties, up to 100,000 of them fatal, are estimated to have been caused by chemicals . . . , a large part following the introduction of mustard gas in 1917.” Kenyon, Why We Need a Chemical Weapons Convention and an OPCW, in The Creation of the Organisation for the Prohibition of Chemical Weapons 1, 4 (I. Kenyon & D. Feakes eds. 2007) (Kenyon & Feakes). The atrocities of that war led the community of nations to adopt the 1925 Geneva Protocol, which prohibited the use of chemicals as a method of warfare. Id., at 5.

Up to the 1990s, however, chemical weapons remained in use both in and out of wartime, with devastating consequences. Iraq’s use of nerve agents and mustard gas during its war with Iran in the 1980s contributed to international support for a renewed, more effective chemical weapons ban. Id., at 6, 10–11. In 1994 and 1995, long-held fears of the use of chemical weapons by terrorists were realized when Japanese extremists carried out two attacks using sarin gas. Id., at 6. The Convention was conceived as an effort to update the Geneva Protocol’s protections and to expand the prohibition on chemical weapons beyond state actors in wartime. Convention Preamble, 1974 U. N. T. S. 318 (the State Parties are “[d]etermined for the sake of all mankind, to exclude completely the possibility of the use of chemical weapons, . . . thereby complementing the obligations assumed under the Geneva Protocol of 1925”). The Convention aimed to achieve that objective by prohibiting the development, stockpiling, or use of chemical weapons by any State Party or person within a State Party’s jurisdiction. Arts. I, II, VII.

It also established an elaborate reporting process requiring State Parties to destroy chemical weapons under their control and submit to inspection and monitoring by an international organization based in The Hague, Netherlands. Arts. VIII, IX.

The Convention provides:

“(1) Each State Party to this Convention undertakes never under any circumstances:

“(a) To develop, produce, otherwise acquire, stockpile or retain chemical weapons, or transfer, directly or indirectly, chemical weapons to anyone;

“(b) To use chemical weapons;

“(c) To engage in any military preparations to use chemical weapons;

“(d) To assist, encourage or induce, in any way, anyone to engage in any activity prohibited to a State Party under this Convention.” Art. I, id., at 319.

“Chemical Weapons” are defined in relevant part as “[t]oxic chemicals and their precursors, except where intended for purposes not prohibited under this Convention, as long as the types and quantities are consistent with such purposes.” Art. II(1)(a), ibid. “Toxic Chemical,” in turn, is defined as “Any chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals. This includes all such chemicals, regardless of their origin or of their method of production, and regardless of whether they are produced in facilities, in munitions or elsewhere.” Art. II(2), id., at 320. “Purposes Not Prohibited Under this Convention” means “[i]ndustrial, agricultural, research, medical, pharmaceutical or other peaceful purposes,” Art. II(9)(a), id., at 322, and other specific purposes not at issue here, Arts. II(9)(b)–(d).

Although the Convention is a binding international agreement, it is “not self-executing.” W. Krutzsch & R. Trapp, A Commentary on the Chemical Weapons Convention 109 (1994). That is, the Convention creates obligations only for State Parties and “does not by itself give rise to domestically enforceable federal law” absent “implementing legislation passed by Congress.” Medellín v. Texas, 552 U. S. 491, 505, n. 2 (2008). It instead provides that “[e]ach State Party shall, in accordance with its constitutional processes, adopt the necessary measures to implement its obligations under this Convention.” Art. VII(1), 1974 U. N. T. S. 331. “In particular,” each State Party shall “[p]rohibit natural and legal persons anywhere . . . under its jurisdiction . . . from undertaking any activity prohibited to a State Party under this Convention, including enacting penal legislation with respect to such activity.” Art. VII (1)(a), id., at 331–332.

Congress gave the Convention domestic effect in 1998 when it passed the Chemical Weapons Convention Implementation Act. See 112 Stat. 2681–856. The Act closely tracks the text of the treaty: It forbids any person knowingly “to develop, produce, otherwise acquire, transfer directly or indirectly, receive, stockpile, retain, own, possess, or use, or threaten to use, any chemical weapon.” 18 U. S. C. §229(a)(1). It defines “chemical weapon” in relevant part as “[a] toxic chemical and its precursors, except where intended for a purpose not prohibited under this chapter as long as the type and quantity is consistent with such a purpose.” §229F(1)(A). “Toxic chemical,” in turn, is defined in general as “any chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals. The term includes all such chemicals, regardless of their origin or of their method of production, and regardless of whether they are produced in facilities, in munitions or elsewhere.” §229F(8)(A). Finally, “purposes not prohibited by this chapter” is defined as “[a]ny peaceful purpose related to an industrial, agricultural, research, medical, or pharmaceutical activity or other activity,” and other specific purposes. §229F(7). A person who violates section 229 may be subject to severe punishment: imprisonment “for any term of years,” or if a victim’s death results, the death penalty or imprisonment “for life.” §229A(a).

B

Petitioner Carol Anne Bond is a microbiologist from Lansdale, Pennsylvania. In 2006, Bond’s closest friend, Myrlinda Haynes, announced that she was pregnant. When Bond discovered that her husband was the child’s father, she sought revenge against Haynes. Bond stole a quantity of 10-chloro-10H-phenoxarsine (an arsenic-based compound) from her employer, a chemical manufacturer. She also ordered a vial of potassium dichromate (a chemical commonly used in printing photographs or cleaning laboratory equipment) on Amazon.com. Both chemicals are toxic to humans and, in high enough doses, potentially lethal. It is undisputed, however, that Bond did not intend to kill Haynes. She instead hoped that Haynes would touch the chemicals and develop an uncomfortable rash.

Between November 2006 and June 2007, Bond went to Haynes’s home on at least 24 occasions and spread the chemicals on her car door, mailbox, and door knob. These attempted assaults were almost entirely unsuccessful. The chemicals that Bond used are easy to see, and Haynes was able to avoid them all but once. On that occasion, Haynes suffered a minor chemical burn on her thumb, which she treated by rinsing with water. Haynes repeatedly called the local police to report the suspicious substances, but they took no action. When Haynes found powder on her mailbox, she called the police again, who told her to call the post office. Haynes did so, and postal inspectors placed surveillance cameras around her home. The cameras caught Bond opening Haynes’s mailbox, stealing an envelope, and stuffing potassium dichromate inside the muffler of Haynes’s car.

Federal prosecutors naturally charged Bond with two counts of mail theft, in violation of 18 U. S. C. §1708. More surprising, they also charged her with two counts of possessing and using a chemical weapon, in violation of section 229(a). Bond moved to dismiss the chemical weapon counts on the ground that section 229 exceeded Congress’s enumerated powers and invaded powers reserved to the States by the Tenth Amendment. The District Court denied Bond’s motion. She then entered a conditional guilty plea that reserved her right to appeal. The District Court sentenced Bond to six years in federal prison plus five years of supervised release, and ordered her to pay a $2,000 fine and $9,902.79 in restitution.

Bond appealed, raising a Tenth Amendment challenge to her conviction. The Government contended that Bond lacked standing to bring such a challenge. The Court of Appeals for the Third Circuit agreed. We granted certiorari, the Government confessed error, and we reversed. We held that, in a proper case, an individual may “assert injury from governmental action taken in excess of the authority that federalism defines.” Bond v. United States, 564 U. S. ___, ___ (2011) (Bond I) (slip op., at 8). We “expresse[d] no view on the merits” of Bond’s constitutional challenge. Id., at ___ (slip op., at 14).

On remand, Bond renewed her constitutional argument. She also argued that section 229 does not reach her conduct because the statute’s exception for the use of chemicals for “peaceful purposes” should be understood in contradistinction to the “warlike” activities that the Convention was primarily designed to prohibit. Bond argued that her conduct, though reprehensible, was not at all “warlike.” The Court of Appeals rejected this argument. 681 F. 3d 149 (CA3 2012). The court acknowledged that the Government’s reading of section 229 would render the statute “striking” in its “breadth” and turn every “kitchen cupboard and cleaning cabinet in America into a potential chemical weapons cache.” Id., at 154, n. 7. But the court nevertheless held that Bond’s use of “‘highly toxic chemicals with the intent of harming Haynes’ can hardly be characterized as ‘peaceful’ under that word’s commonly understood meaning.” Id., at 154 (citation omitted).

The Third Circuit also rejected Bond’s constitutional challenge to her conviction, holding that section 229 was “necessary and proper to carry the Convention into effect.” Id., at 162. The Court of Appeals relied on this Court’s opinion in Missouri v. Holland, 252 U. S. 416 (1920), which stated that “[i]f the treaty is valid there can be no dispute about the validity of the statute” that implements it “as a necessary and proper means to execute the powers of the Government,” id., at 432.

We again granted certiorari, 568 U. S. ___ (2013).

II

In our federal system, the National Government possesses only limited powers; the States and the people retain the remainder. The States have broad authority to enact legislation for the public good—what we have often called a “police power.” United States v. Lopez, 514 U. S. 549, 567 (1995). The Federal Government, by contrast, has no such authority and “can exercise only the powers granted to it,” McCulloch v. Maryland, 4 Wheat. 316, 405 (1819), including the power to make “all Laws which shall be necessary and proper for carrying into Execution” the enumerated powers, U. S. Const., Art. I, §8, cl. 18. For nearly two centuries it has been “clear” that, lacking a police power, “Congress cannot punish felonies generally.” Cohens v. Virginia, 6 Wheat. 264, 428 (1821). A criminal act committed wholly within a State “cannot be made an offence against the United States, unless it have some relation to the execution of a power of Congress, or to some matter within the jurisdiction of the United States.” United States v. Fox, 95 U. S. 670, 672 (1878).

The Government frequently defends federal criminal legislation on the ground that the legislation is authorized pursuant to Congress’s power to regulate interstate commerce. In this case, however, the Court of Appeals held that the Government had explicitly disavowed that argument before the District Court. 681 F. 3d, at 151, n. 1. As a result, in this Court the parties have devoted significant effort to arguing whether section 229, as applied to Bond’s offense, is a necessary and proper means of executing the National Government’s power to make treaties. U. S. Const., Art. II, §2, cl. 2. Bond argues that the lower court’s reading of Missouri v. Holland would remove all limits on federal authority, so long as the Federal Government ratifies a treaty first. She insists that to effectively afford the Government a police power whenever it implements a treaty would be contrary to the Framers’ careful decision to divide power between the States and the National Government as a means of preserving liberty. To the extent that Holland authorizes such usurpation of traditional state authority, Bond says, it must be either limited or overruled.

The Government replies that this Court has never held that a statute implementing a valid treaty exceeds Congress’s enumerated powers. To do so here, the Government says, would contravene another deliberate choice of the Framers: to avoid placing subject matter limitations on the National Government’s power to make treaties. And it might also undermine confidence in the United States as an international treaty partner.

Notwithstanding this debate, it is “a well-established principle governing the prudent exercise of this Court’s jurisdiction that normally the Court will not decide a constitutional question if there is some other ground upon which to dispose of the case.” Escambia County v. McMillan, 466 U. S. 48, 51 (1984) (per curiam); see also Ashwander v. TVA, 297 U. S. 288, 347 (1936) (Brandeis, J., concurring). Bond argues that section 229 does not cover her conduct. So we consider that argument first.

III

Section 229 exists to implement the Convention, so we begin with that international agreement. As explained, the Convention’s drafters intended for it to be a comprehensive ban on chemical weapons. But even with its broadly worded definitions, we have doubts that a treaty about chemical weapons has anything to do with Bond’s conduct. The Convention, a product of years of worldwide study, analysis, and multinational negotiation, arose in response to war crimes and acts of terrorism. See Kenyon & Feakes 6. There is no reason to think the sovereign nations that ratified the Convention were interested in anything like Bond’s common law assault.

Even if the treaty does reach that far, nothing prevents Congress from implementing the Convention in the same manner it legislates with respect to innumerable other matters—observing the Constitution’s division of responsibility between sovereigns and leaving the prosecution of purely local crimes to the States. The Convention, after all, is agnostic between enforcement at the state versus federal level: It provides that “[e]ach State Party shall, in accordance with its constitutional processes, adopt the necessary measures to implement its obligations under this Convention.” Art. VII(1), 1974 U. N. T. S. 331 (emphasis added); see also Tabassi, National Implementation: Article VII, in Kenyon & Feakes 205, 207 (“Since the

creation of national law, the enforcement of it and the structure and administration of government are all sovereign acts reserved exclusively for [State Parties], it is not surprising that the Convention is so vague on the critical matter of national implementation.”).

Fortunately, we have no need to interpret the scope of the Convention in this case. Bond was prosecuted under section 229, and the statute—unlike the Convention— must be read consistent with principles of federalism inherent in our constitutional structure.

A

In the Government’s view, the conclusion that Bond “knowingly” “use[d]” a “chemical weapon” in violation of section 229(a) is simple: The chemicals that Bond placed on Haynes’s home and car are “toxic chemical[s]” as defined by the statute, and Bond’s attempt to assault Haynes was not a “peaceful purpose.” §§229F(1), (8), (7). The problem with this interpretation is that it would “dramatically intrude[] upon traditional state criminal jurisdiction,” and we avoid reading statutes to have such reach in the absence of a clear indication that they do. United States v. Bass, 404 U. S. 336, 350 (1971).

Part of a fair reading of statutory text is recognizing that “Congress legislates against the backdrop” of certain unexpressed presumptions. EEOC v. Arabian American Oil Co., 499 U. S. 244, 248 (1991). As Justice Frankfurter put it in his famous essay on statutory interpretation, correctly reading a statute “demands awareness of certain presuppositions.” Some Reflections on the Reading of Statutes, 47 Colum. L. Rev. 527, 537 (1947). For example, we presume that a criminal statute derived from the common law carries with it the requirement of a culpable mental state—even if no such limitation appears in the text—unless it is clear that the Legislature intended to impose strict liability. United States v. United States Gypsum Co., 438 U. S. 422, 437 (1978). To take another example, we presume, absent a clear statement from Congress, that federal statutes do not apply outside the United States. Morrison v. National Australia Bank Ltd., 561 U. S. 247, 255 (2010). So even though section 229, read on its face, would cover a chemical weapons crime if committed by a U. S. citizen in Australia, we would not apply the statute to such conduct absent a plain statement from Congress.¹ The notion that some things “go without saying” applies to legislation just as it does to everyday life.

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¹Congress has in fact included just such a plain statement in section 229(c)(2): “Conduct prohibited by [section 229(a)] is within the jurisdiction of the United States if the prohibited conduct . . . takes place outside of the United States and is committed by a national of the United States.”

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Among the background principles of construction that our cases have recognized are those grounded in the relationship between the Federal Government and the States under our Constitution. It has long been settled, for example, that we presume federal statutes do not abrogate state sovereign immunity, Atascadero State Hospital v. Scanlon, 473 U. S. 234, 243 (1985), impose obligations on the States pursuant to section 5 of the Fourteenth Amendment, Pennhurst State School and Hospital v. Halderman, 451 U. S. 1, 16–17 (1981), or preempt state law, Rice v. Santa Fe Elevator Corp., 331 U. S. 218, 230 (1947). Closely related to these is the well-established principle that “‘it is incumbent upon the federal courts to be certain of Congress’ intent before finding that federal law overrides’” the “usual constitutional balance of federal and state powers.” Gregory v. Ashcroft, 501 U. S. 452, 460 (1991) (quoting Atascadero, supra, at 243). To quote Frankfurter again, if the Federal Government would “‘radically readjust[] the balance of state and national authority, those charged with the duty of legislating [must be] reasonably explicit’ ” about it. BFP v. Resolution Trust Corporation, 511 U. S. 531, 544 (1994) (quoting Some Reflections, supra, at 539–540; second alteration in original). Or as explained by Justice Marshall, when legislation “affect[s] the federal balance, the requirement of clear statement assures that the legislature has in fact faced, and intended to bring into issue, the critical matters involved in the judicial decision.” Bass, supra, at 349.

We have applied this background principle when construing federal statutes that touched on several areas of traditional state responsibility. See Gregory, supra, at 460 (qualifications for state officers); BFP, supra, at 544 (titles to real estate); Solid Waste Agency of Northern Cook Cty. v. Army Corps of Engineers, 531 U. S. 159, 174 (2001) (land and water use). Perhaps the clearest example of traditional state authority is the punishment of local criminal activity. United States v. Morrison, 529 U. S. 598, 618 (2000). Thus, “we will not be quick to assume that Congress has meant to effect a significant change in the sensitive relation between federal and state criminal jurisdiction.” Bass, 404 U. S., at 349.

In Bass, we interpreted a statute that prohibited any convicted felon from “‘receiv[ing], possess[ing], or transport[ing] in commerce or affecting commerce . . . any firearm.’” Id., at 337. The Government argued that the statute barred felons from possessing all firearms and that it was not necessary to demonstrate a connection to interstate commerce. We rejected that reading, which would “render[] traditionally local criminal conduct a matter for federal enforcement and would also involve a substantial extension of federal police resources.” Id., at 350. We instead read the statute more narrowly to require proof of a connection to interstate commerce in every case, thereby “preserv[ing] as an element of all the offenses a requirement suited to federal criminal jurisdiction alone.” Id., at 351.

Similarly, in Jones v. United States, 529 U. S. 848, 850 (2000), we confronted the question whether the federal arson statute, which prohibited burning “‘any . . . property used in interstate or foreign commerce or in any activity affecting interstate or foreign commerce,’” reached an owner-occupied private residence. Once again we rejected the Government’s “expansive interpretation,” under which “hardly a building in the land would fall outside the federal statute’s domain.” Id., at 857. We instead held that the statute was “most sensibly read” more narrowly to reach only buildings used in “active employment for commercial purposes.” Id., at 855. We noted that “arson is a paradigmatic common-law state crime,” id., at 858, and that the Government’s proposed broad reading would “‘significantly change[] the federal-state balance,’” ibid. (quoting Bass , 404 U. S., at 349), “mak[ing] virtually every arson in the country a federal offense,” 529 U. S., at 859.

These precedents make clear that it is appropriate to refer to basic principles of federalism embodied in the Constitution to resolve ambiguity in a federal statute. In this case, the ambiguity derives from the improbably broad reach of the key statutory definition given the term—“chemical weapon”—being defined; the deeply serious consequences of adopting such a boundless reading; and the lack of any apparent need to do so in light of the context from which the statute arose—a treaty about chemical warfare and terrorism. We conclude that, in this curious case, we can insist on a clear indication that Congress meant to reach purely local crimes, before interpreting the statute’s expansive language in a way that intrudes on the police power of the States. See Bass, supra, at 349.²

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²JUSTICE SCALIA contends that the relevance of Bass and Jones to this case is “entirely made up,” post, at 3 (opinion concurring in judgment), but not because he disagrees with interpreting statutes in light of principles of federalism. Rather, he says that Bass was a case where the statute was unclear. We agree; we simply think the statute in this case is also subject to construction, for the reasons given. As for Jones, JUSTICE SCALIA argues that the discussion of federalism in that case was beside the point. Post, at 4. We do not read Jones that way; the Court adopted the “most sensibl[e] read[ing]” of the statute, 529 U. S., at 855, which suggests that other sensible readings were possible. In arriving at its fair reading of the statute, the Court considered the dramatic extent to which the Government’s broader interpretation would have expanded “the federal statute’s domain.” Id., at 857. We do the same here.

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B

We do not find any such clear indication in section 229. “Chemical weapon” is the key term that defines the statute’s reach, and it is defined extremely broadly. But that general definition does not constitute a clear statement that Congress meant the statute to reach local criminal conduct.

In fact, a fair reading of section 229 suggests that it does not have as expansive a scope as might at first appear. To begin, as a matter of natural meaning, an educated user of English would not describe Bond’s crime as involving a “chemical weapon.” Saying that a person “used a chemical weapon” conveys a very different idea than saying the person “used a chemical in a way that caused some harm.” The natural meaning of “chemical weapon” takes account of both the particular chemicals that the defendant used and the circumstances in which she used them.

When used in the manner here, the chemicals in this case are not of the sort that an ordinary person would associate with instruments of chemical warfare. The substances that Bond used bear little resemblance to the deadly toxins that are “of particular danger to the objectives of the Convention.” Why We Need a Chemical Weapons Convention and an OPCW, in Kenyon & Feakes 17 (describing the Convention’s Annex on Chemicals, a nonexhaustive list of covered substances that are subject to special regulation). More to the point, the use of something as a “weapon” typically connotes “[a]n instrument of offensive or defensive combat,” Webster’s Third New International Dictionary 2589 (2002), or “[a]n instrument of attack or defense in combat, as a gun, missile, or sword,” American Heritage Dictionary 2022 (3d ed. 1992). But no speaker in natural parlance would describe Bond’s feud-driven act of spreading irritating chemicals on Haynes’s door knob and mailbox as “combat.” Nor do the other circumstances of Bond’s offense—an act of revenge born of romantic jealousy, meant to cause discomfort, that produced nothing more than a minor thumb burn—suggest that a chemical weapon was deployed in Norristown, Pennsylvania. Potassium dichromate and 10-chloro-10H-phenoxarsine might be chemical weapons if used, say, to poison a city’s water supply. But Bond’s crime is worlds apart from such hypotheticals, and covering it would give the statute a reach exceeding the ordinary meaning of the words Congress wrote.

In settling on a fair reading of a statute, it is not unusual to consider the ordinary meaning of a defined term, particularly when there is dissonance between that ordinary meaning and the reach of the definition. In Johnson v. United States, 559 U. S. 133, 136 (2010), for example, we considered the statutory term “‘violent felony,’” which the Armed Career Criminal Act defined in relevant part as an offense that “‘has as an element the use . . . of physical force against the person of another.’” Although “physical force against . . . another” might have meant any force, however slight, we thought it “clear that in the context of a statutory definition of ‘violent felony,’ the phrase ‘physical force’ means violent force—that is, force capable of

causing physical pain or injury to another person.” Id., at 140. The ordinary meaning of “chemical weapon” plays a similar limiting role here.

The Government would have us brush aside the ordinary meaning and adopt a reading of section 229 that would sweep in everything from the detergent under the kitchen sink to the stain remover in the laundry room. Yet no one would ordinarily describe those substances as “chemical weapons.” The Government responds that because Bond used “specialized, highly toxic” (though legal) chemicals, “this case presents no occasion to address whether Congress intended [section 229] to apply to common household substances.” Brief for United States 13, n. 3. That the statute would apply so broadly, however, is the inescapable conclusion of the Government’s position: Any parent would be guilty of a serious federal offense—possession of a chemical weapon—when, exasperated by the children’s repeated failure to clean the goldfish tank, he considers poisoning the fish with a few drops of vinegar. We are reluctant to ignore the ordinary meaning of “chemical weapon” when doing so would transform a statute passed to implement the international Convention on Chemical Weapons into one that also makes it a federal offense to poison goldfish. That would not be a “realistic assessment[] of congressional intent.” Post, at 6 (SCALIA, J., concurring in judgment).

In light of all of this, it is fully appropriate to apply the background assumption that Congress normally preserves “the constitutional balance between the National Government and the States.” Bond I, 564 U. S., at ___ (slip op., at 10). That assumption is grounded in the very structure of the Constitution. And as we explained when this case was first before us, maintaining that constitutional balance is not merely an end unto itself. Rather, “[b]y denying any one government complete jurisdiction over all the concerns of public life, federalism protects the liberty of the individual from arbitrary power.” Ibid.

The Government’s reading of section 229 would “‘alter sensitive federal-state relationships,’” convert an astonishing amount of “traditionally local criminal conduct” into “a matter for federal enforcement,” and “involve a substantial extension of federal police resources.” Bass, 404 U. S., at 349–350. It would transform the statute from one whose core concerns are acts of war, assassination, and terrorism into a massive federal anti-poisoning regime that reaches the simplest of assaults. As the Government reads section 229, “hardly” a poisoning “in the land would fall outside the federal statute’s domain.” Jones, 529 U. S., at 857. Of course Bond’s conduct is serious and unacceptable—and against the laws of Pennsylvania. But the background principle that Congress does not normally intrude upon the police power of the States is critically important. In light of that principle, we are reluctant to conclude that Congress meant to punish Bond’s crime with a federal prosecution for a chemical weapons attack.

In fact, with the exception of this unusual case, the Federal Government itself has not looked to section 229 to reach purely local crimes. The Government has identified only a handful of prosecutions that have been brought under this section. Brief in Opposition 27, n. 5. Most of those involved either terrorist plots or the possession of extremely dangerous substances with the potential to cause severe harm to many people. See United States v. Ghane, 673 F. 3d 771 (CA8 2012) (defendant possessed enough potassium cyanide to kill 450 people); United States v. Crocker, 260 Fed. Appx. 794 (CA6 2008) (defendant attempted to acquire VX nerve gas and chlorine gas as part of a plot to attack a federal courthouse); United States v. Krar, 134 Fed. Appx. 662 (CA5 2005) (per curiam) (defendant possessed sodium cyanide); United States v. Fries, 2012 WL 689157 (D Ariz., Feb. 28, 2012) (defendant set off a homemade chlorine bomb in the victim’s driveway, requiring evacuation of a residential neighborhood). The Federal Government undoubtedly has a substantial interest in enforcing criminal laws against assassination, terrorism, and acts with the potential to cause mass suffering. Those crimes have not traditionally been left predominantly to the States, and nothing we have said here will disrupt the Government’s authority to prosecute such offenses.

It is also clear that the laws of the Commonwealth of Pennsylvania (and every other State) are sufficient to prosecute Bond. Pennsylvania has several statutes that would likely cover her assault. See 18 Pa. Cons. Stat. §§2701 (2012) (simple assault), 2705 (reckless endangerment), 2709 (harassment). ³ And state authorities regularly enforce these laws in poisoning cases. See, e.g., Gamiz, Family Survives Poisoned Burritos, Allentown, Pa., Morning Call, May 18, 2013 (defendant charged with assault, reckless endangerment, and harassment for feeding burritos poisoned with prescription medication to her husband and daughter); Cops: Man Was Poisoned Over 3 Years, Harrisburg, Pa., Patriot News, Aug. 12, 2012, p. A11 (defendant charged with assault and reckless endangerment for poisoning a man with eye drops over three years so that “he would pay more attention to her”).

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³Pennsylvania also prohibits using “a weapon of mass destruction,” including a “chemical agent.” 18 Pa. Cons. Stat. §§2716(a), (i). Just as we conclude that Bond’s offense cannot be fairly described as the use of a chemical weapon, Pennsylvania authorities apparently determined that her crime did not involve a “weapon of mass destruction.”

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The Government objects that Pennsylvania authorities charged Bond with only a minor offense based on her “harassing telephone calls and letters,” Bond I, 564 U. S., at ___ (slip op., at 2), and declined to prosecute her for assault. But we have traditionally viewed the exercise of state officials’ prosecutorial discretion as a valuable feature of our constitutional system. See Bordenkircher v. Hayes, 434 U. S. 357, 364 (1978). And nothing in the Convention shows a clear intent to abrogate that feature. Prosecutorial discretion involves carefully weighing the benefits of a prosecution against the evidence needed to convict, the resources of the public fisc, and the public policy of the State. Here, in its zeal to prosecute Bond, the Federal Government has “displaced” the “public policy of the Commonwealth of Pennsylvania, enacted in its capacity as sovereign,” that Bond does not belong in prison for a chemical weapons offense. Bond I, supra, at ___ (slip op., at 12); see also Jones, supra, at 859 (Stevens, J., concurring) (federal prosecution of a traditionally local crime “illustrates how a criminal law like this may effectively displace a policy choice made by the State”).

As we have explained, “Congress has traditionally been reluctant to define as a federal crime conduct readily denounced as criminal by the States.” Bass, 404 U. S., at 349. There is no clear indication of a contrary approach here. Section 229 implements the Convention, but Bond’s crime could hardly be more unlike the uses of mustard gas on the Western Front or nerve agents in the Iran-Iraq war that form the core concerns of that treaty. See Kenyon & Feakes 6. There are no life-sized paintings of Bond’s rival washing her thumb. And there are no apparent interests of the United States Congress or the community of nations in seeing Bond end up in federal prison, rather than dealt with (like virtually all other criminals in Pennsylvania) by the State. The Solicitor General acknowledged as much at oral argument. See Tr. of Oral Arg. 47 (“I don’t think anybody would say [that] whether or not Ms. Bond is prosecuted would give rise to an international incident”).

This case is unusual, and our analysis is appropriately limited. Our disagreement with our colleagues reduces to whether section 229 is “utterly clear.” Post, at 5 (SCALIA, J., concurring in judgment). We think it is not, given that the definition of “chemical weapon” in a particular case can reach beyond any normal notion of such a weapon, that the context from which the statute arose demonstrates a much more limited prohibition was intended, and that the most sweeping reading of the statute would fundamentally upset the Constitution’s balance between national and local power. This exceptional convergence of factors gives us serious reason to doubt the Government’s expansive reading of section 229, and calls for us to interpret the statute more narrowly.

In sum, the global need to prevent chemical warfare does not require the Federal Government to reach into the kitchen cupboard, or to treat a local assault with a chemical irritant as the deployment of a chemical weapon. There is no reason to suppose that Congress—in implementing the Convention on Chemical Weapons—thought otherwise.

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The Convention provides for implementation by each ratifying nation “in accordance with its constitutional processes.” Art. VII(1), 1974 U. N. T. S. 331. As James Madison explained, the constitutional process in our “compound republic” keeps power “divided between two distinct governments.” The Federalist No. 51, p. 323 (C. Rossiter ed. 1961). If section 229 reached Bond’s conduct, it would mark a dramatic departure from that constitutional structure and a serious reallocation of criminal law enforcement authority between the Federal Government and the States. Absent a clear statement of that purpose, we will not presume Congress to have authorized such a stark intrusion into traditional state authority.

The judgment of the Court of Appeals is reversed, and the case is remanded for further proceedings consistent with this opinion.

It is so ordered

ROBERTS, C. J., delivered the opinion of the Court, in which KENNEDY, GINSBURG, BREYER, SOTOMAYOR, and KAGAN, JJ., joined. SCALIA, J., filed an opinion concurring in the judgment, in which THOMAS, J., joined, and in which ALITO, J., joined as to Part I. THOMAS, J., filed an opinion concurring in the judgment, in which SCALIA, J., joined, and in which ALITO, J., joined as to Parts I, II, and III. ALITO, J., filed an opinion concurring in the judgment.

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JUSTICE SCALIA, with whom JUSTICE THOMAS joins, and with whom JUSTICE ALITO joins as to Part I, concurring in the judgment.

Somewhere in Norristown, Pennsylvania, a husband’s paramour suffered a minor thumb burn at the hands of a betrayed wife. The United States Congress—“every where extending the sphere of its activity, and drawing all power into its impetuous vortex”¹ —has made a federal case out of it. What are we to do?

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¹The Federalist No. 48, p. 333 (J. Cooke ed. 1961) (J. Madison) (hereinafter The Federalist).

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It is the responsibility of “the legislature, not the Court, . . . to define a crime, and ordain its punishment.” United States v. Wiltberger, 5 Wheat. 76, 95 (1820) (Marshall, C.J., for the Court). And it is “emphatically the province and duty of the judicial department to say what the law [including the Constitution] is.” Marbury v. Madison, 1 Cranch 137, 177 (1803) (same). Today, the Court shirks its job and performs Congress’s. As sweeping and unsettling as the Chemical Weapons Convention Implementation Act of 1998 may be, it is clear beyond doubt that it covers what Bond did; and we have no authority to amend it. So we are forced to decide—there is no way around it—whether the Act’s application to what Bond did was constitutional.

I would hold that it was not, and for that reason would reverse the judgment of the Court of Appeals for the Third Circuit.

I.

The Statutory Question

A. Unavoidable Meaning of the Text

The meaning of the Act is plain. No person may knowingly “develop, produce, otherwise acquire, transfer directly or indirectly, receive, stockpile, retain, own, possess, or use, or threaten to use, any chemical weapon.” 18 U. S. C. §229(a)(1). A “chemical weapon” is “[a] toxic chemical and its precursors, except where intended for a purpose not prohibited under this chapter as long as the type and quantity is consistent with such a purpose.” §229F(1)(A). A “toxic chemical” is “any chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals. The term includes all such chemicals, regardless of their origin or of their method of production, and regardless of whether they are produced in facilities, in munitions or elsewhere.” §229F(8)(A). A “purpose not prohibited” is “[a]ny peaceful purpose related to an industrial, agricultural, research, medical, or pharmaceutical activity or other activity.” §229F(7)(A).

Applying those provisions to this case is hardly complicated. Bond possessed and used “chemical[s] which through [their] chemical action on life processes can cause death, temporary incapacitation or permanent harm.” Thus, she possessed “toxic chemicals.” And, because they were not possessed or used only for a “purpose not prohibited,” §229F(1)(A), they were ere not possessed or used only for a “purpose not prohibited,” §229F(1)(A), they were “chemical weapons.” Ergo, Bond violated the Act. End of statutory analysis, I would have thought.

The Court does not think the interpretive exercise so simple. But that is only because its result-driven anti-textualism befogs what is evident.

B.

The Court’s Interpretation

The Court’s account of the clear-statement rule reads like a really good lawyer’s brief for the wrong side, relying on cases that are so close to being on point that someone eager to reach the favored outcome might swallow them. The relevance to this case of United States v. Bass, 404 U.S. 336 (1971), and Jones v. United States, 529 U. S. 848 (2000), is, in truth, entirely made up. . . . [The rest of this section is omitted.]

C.

The Statute as Judicially Amended

I suspect the Act will not survive today’s gruesome surgery. A criminal statute must clearly define the conduct it proscribes. If it does not “‘give a person of ordinary intelligence fair notice’ ” of its scope, United States v. Batchelder, 442 U. S. 114, 123 (1979), it denies due process.

The new §229(a)(1) fails that test. . . . [The rest of this section is omitted.]

II. The Constitutional Question

Since the Act is clear, the real question this case presents is whether the Act is constitutional as applied to petitioner. An unreasoned and citation-less sentence from our opinion in Missouri v. Holland, 252 U. S. 416 (1920), purported to furnish the answer: “If the treaty is valid”—and no one argues that the Convention is not—“there can be no dispute about the validity of the statute under Article I, §8, as a necessary and proper means to execute the powers of the Government.” Id., at 432. Petitioner and her amici press us to consider whether there is anything to this ipse dixit. The Constitution’s text and structure show that there is not. [Footnotes omitted.]

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