U.S. Supreme Court arguments over the constitutional power to make and implement treaties took a dramatic turn Tuesday when Solicitor General Donald Verrilli Jr. warned justices that a ruling interpreting the meaning of a chemical weapons treaty would be “terribly unfortunate” and could disrupt “very sensitive negotiations” underway with Syria and other nations.

Verrilli’s statement seemed to irritate the court, which does not usually like to be told that it should steer clear of an important issue in a pending case. Justice Stephen Breyer, usually an ally of the Obama administration, told Verrilli with annoyance that if national security was at stake in the dispute, “the State Department better file a brief” saying so. “Is that what you are telling me,” Breyer added incredulously, “that if I write the opinion that I think the law requires me to write, that I am somehow hurting the national security interest of the United States?”

The exchange was not the only signal that the administration may have difficulty winning in the case of Bond v. United States, which began as a “lover’s triangle” dispute from Pennsylvania but has mushroomed into a major test of the power of Congress to implement international treaties in ways that may interfere with the prerogatives of the 50 states. The government argues that the treaty power is a core function of the national government, giving Congress broad power to make treaties work.

When Carol Bond of Lansdale, Pa., learned in 2006 that her husband had impregnated her best friend Myrlinda Haynes, she sought revenge by, among other things, spreading toxic chemicals on Haynes’ mailbox, car door and other surfaces she might touch. Haynes discovered the chemicals and complained to state police, but they took no action. Federal postal inspectors did, however, charging Bond with violating a federal law passed to implement an international treaty banning the use of chemical weapons — the same treaty invoked to destroy Syria’s chemical weapons.

Arguing for Bond, former solicitor general Paul Clement said that using the federal law against his client violates the Constitution because “Congress lacks general police power,” and cannot prosecute offenses like Bond’s unless the federal government can show jurisdiction or some national interest at stake. More broadly, Clement argued that authority given to Congress to enact laws implementing treaties does not mean Congress can give itself powers that are not otherwise spelled out in the Constitution.

Justices Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor quickly challenged Clement, who had conceded in his brief that the chemical weapons treaty itself was constitutional, even if the implementing statute was not. The language of the law mirrors the treaty, Ginsburg said, so it is a “puzzle” how one could pass muster and the other could not. Kagan asserted that the Constitution’s framers placed no “subject-matter limitations” on the treaty power, so she wondered how the law could be unconstitutional. For her part, Sotomayor said it would be “deeply ironic” if the Supreme Court overturned a law that implements the same treaty that is being used in criticizing Syria.

Sotomayor was the first, but not the last, participant in Tuesday’s argument to cite the situation in Syria. Current events outside the four corners of a specific case before the court are rarely mentioned during argument. But the broader reach of a decision in the Bond case was clearly on justices’ minds.

Clement stuck to his position that the statute implementing the chemical weapons treaty interferes with the federal-state balance established by the Constitution. “The states are absolutely ready and able” to handle situations like the Bond matter without invoking the chemical weapons treaty, he said. But Ginsburg replied, “there’s an irony in what you said,” because state police turned Haynes away “a dozen times,” and she only got a response when she went to postal inspectors. Clement dismissed that as an example of “prosecutorial discretion” that could not be viewed as a violation of the treaty.

At one point, Clement did offer the court a way to save the statute through a “narrowing construction,” pointing to an exemption in the treaty that allows use of chemicals for “peaceful purposes.” While what Bond did could have been prosecuted locally under criminal laws, Clement said, her behavior was not “war-like” and therefore could be deemed outside the scope of the implementing law.

It was that offer from Clement that triggered Verrilli’s dramatic statement. The issue of which uses of chemicals are warlike and which are peaceful under the treaty, Verrilli said, is “one of the very things we are trying to sort out right now in Syria.” Similar language appears in nuclear nonproliferation treaties as well, Verrilli said, and “we’re engaged in very sensitive negotiations right now” on that point. A Supreme Court interpretation of what activities are or are not warlike, he said, “could have an unfortunate bearing” on those negotiations.

Clement seemed to acknowledge that his compromise way of allowing the statute to stand would not work because, as Verrilli had warned, that would interfere with administration policy in Syria. The only option left for the court, Clement said, was to find that the statute is “simply unconstitutional,” Clement said.

Verrilli resisted repeated requests by justices for guidance in determining when, or whether, a law implementing a treaty could be so far removed from the enumerated powers of Congress that it would be unconstitutional. “There may well be a line to be drawn,” Verrilli said, but the court did not have to find it in the Bond case. Justices bombarded him with hypotheticals, including one from Justice Antonin Scalia: If the Senate approved, and the president signed, an international treaty requiring participating countries to allow same-sex marriage, an implementing statute would amount to a federal marriage law — inserting the federal government into family law issues that have long been the province of states.

Justice Samuel Alito Jr. offered another example to demonstrate that the chemical weapons law has “enormous breadth,” covering use of any chemicals that can cause death or injury to a person or animal. “Would it shock you if I would you that a few days ago, my wife and I distributed toxic chemicals to a great number of children?” Alito asked Verrilli, going on to explain that Halloween candy containing chocolate could be viewed as poisonous to dogs.

Amid laughter and subsequent talk about horses eating poisoned potatoes, Verrilli sternly brought the discussion back to the issue at hand. “This is serious business,” he said disapprovingly. “There is a real risk in courts getting involved in defining the line between warlike and peaceful purposes. … [It] is going to undermine the ability of our negotiators to make treaties.”

Contact Tony Mauro at tmauro@alm.com.