A law passed by Congress to give domestic effect to an international chemical weapons treaty does not apply to the case of Carol Anne Bond, who used harmful chemicals to cause a minor burn on the thumb of a woman who slept with her husband. That's according to the Supreme Court's unanimous ruling in Bond v. U.S. In his majority opinion, Chief Justice John Roberts wrote that "the global need to prevent chemical warfare does not require the Federal Government to reach into the kitchen cupboard." 

The law in question here is the Chemical Weapons Convention Implementation Act of 1998, which forbids anyone from “possess[ ing] or use[ing] . . . any chemical weapon,” where a chemical weapon is defined as a "toxic chemical or its precursors." It's a law passed by Congress to domestically enact the "International Convention on the Prohibition of the Development, Production, Stockpiling, and Use of Chemical Weapons and on Their Destruction," an international treaty. While the court seems to have avoided making a decision on whether the Chemical Weapons Act is itself a result of an unconstitutional congressional overstep, it did rule that the law does not apply to Bond's poisoning attempt. To make this point, Roberts began his opinion with a reference to a painting that does show the effects of actual chemical weapons use: John Singer Sargent's Gassed

By contrast, Bond, after discovering Myrlinda Haynes's affair with her husband, spread a mixture of toxic chemicals that would produced a burn on contact on places she thought Haynes might touch, like a doorknob or a car door handle. Bond is a microbiologist, and one of the chemicals used was stolen from the manufacturer for whom she worked. Although the revenge attempt only produced a single, minor burn on Haynes's hand — she treated it with running water — Bond was charged federally with mail theft and under the federal Chemical Weapons Convention Implementation Act. Roberts wrote, however, that "we have doubts that a treaty about chemical weapons has anything to do with Bond’s conduct...There is no reason to think the sovereign nations that ratified the Convention were interested in  anything like Bond’s common law assault," adding that Pennsylvania law should have been "sufficient" to punish Bond's criminal conduct. 

Roberts also gave an example of what he believes could happen if the chemical weapons law is given a particularly broad interpretation: 

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.” 

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.  

Although the court unanimously concurred that Bond's conviction under the chemical weapons law should be thrown out, some of the conservatives on the bench (Justices Samuel Alito, Antonin Scalia and Clarence Thomas) said separately that they would have liked to use the case to address the more controversial question of Congress's treaty powers. 

Here's the full opinion

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