SCOTUSblog has a nice summary of the intense questioning on both sides:
But Verrilli seemed to be tested more rigorously in trying to persuade the Court not to start drawing lines to limit treaty power or treaty implementation, as the more conservative Justices — sometimes using sarcasm — challenged his core argument. The conservatives were joined in their challenges by Justice Stephen G. Breyer, who often is a strong defender of national government power.
But it was Breyer who seemed to irritate Verrilli the most, when the Justice discussed how open-ended the weapons treaty was — so much so that it might even reach disgraced cyclist Lance Armstrong’s use of performance-enhancing drugs — and pressed Verrilli to say what limits, if any, there were on the treaty’s reach. “Hypotheticals are just hypotheticals; they are not real cases,” Verrilli shot back.
Verrilli, though, also had to face some tart responses. Justice Samuel A. Alito, Jr., said that the hypotheticals the Justices were reciting were not real cases “because you haven’t prosecuted them.” Alito went on to test the government position by noting that, a few days ago, he and his wife had passed out “chemical weapons” to children — that is, Halloween chocolate. He noted that “chocolate is poisonous to dogs,” and the treaty bans the use of any chemical harmful to animals as well as humans.
When Justice Breyer commented lightly that “there was chocolate all over the place,” Verrilli bluntly commented: “This is serious business.”
Chief Justice John G. Roberts, Jr., repeatedly questioned the Solicitor General about whether there is any constitutional limit on Congress’s power to enter treaties or implement them, and whether a treaty could give Congress the authority to claim ”national police powers.” Verrilli answered that it would be ”unimaginable that the Senate would ratify” such a treaty.
But that answer prompted Justice Anthony M. Kennedy to say: “It seems unimaginable that you did bring this prosecution (of Carol Bond).”
Justice Antonin Scalia even brought into the argument the current controversy over same-sex marriage, suggesting that the government’s argument was so sweeping that the U.S. could join in a treaty approving same-sex marriage, and requiring Congress to pass a law making that binding nationally, on all of the states. Verrilli, Scalia suggested, was trying to “drag Congress into areas where it has never been before.” The Solicitor General answered that the Constitution’s structure, with checks and balances, put limits on treaty-making and treaty-implementation.
Verrilli argued that there was no dispute over whether the chemical weapons treaty was valid, so the implementing law should be, too, because “there is no daylight” between what each covered. But Justice Scalia directly disputed the point, saying the implementing law went considerably further.
All of the pundits are concluding that the Court will rule for Bond, which would be fantastic. It's time to start reigning in the federal prosecution of local crime. We'll see.