The international Convention on Chemical Weapons 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. Congress enacted the Chemical Weapons Convention Implementation Act of 1998. The Act 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.” 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 are consistent with such a purpose.” “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.” D is a microbiologist. D’s closest friend, Myrlinda Haynes, announced that she was pregnant. D's husband was the child’s father. D 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. D did not intend to kill Haynes. D hoped that Haynes would touch the chemicals and develop an uncomfortable rash. D went to Haynes’s home on at least 24 occasions and spread the chemicals on her car door, mailbox, and doorknob. The chemicals are easy to see, and Haynes was able to avoid them all but once. D 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 D in the act of opening Haynes’s mailbox, stealing an envelope, and stuffing potassium dichromate inside the muffler of Haynes’s car. D was charged with two counts of mail theft, in violation of 18 U.S.C. § 1708. They also charged her with two counts of possessing and using a chemical weapon, in violation of section 229(a). D claimed that section 229 exceeded Congress’s enumerated powers and invaded powers reserved to the States by the Tenth Amendment. D entered a conditional guilty plea that reserved her right to appeal. The District Court sentenced D 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. D appealed. P contended that D lacked standing to bring a Tenth Amendment challenge. The Court of Appeals for the Third Circuit agreed. The Supreme Court granted certiorari and reversed. It held that in a proper case, an individual may “assert injury from governmental action taken in excess of the authority that federalism defines.” On remand, D 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 ruled for P even though it 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.” It held that section 229 was “necessary and proper to carry the Convention into effect.” The Supreme Court granted certiorari again.