I was surprised that no one (that I noticed) made the argument that the legislation in United States v. Bond was "necessary and proper to carry into execution the executive power." After all, a non-self-executing treaty is still the law of the land per the supremacy clause, so the President has a duty to faithfully execute it as part of his executive power. (See this 2008 article by Edward Swaine).
That seems like a stronger argument than that the legislation was necessary and proper to carry into execution the power to make treaties, given that the chemical weapons convention was made without much help from the subsequent implementing legislation. It could be argued that the parties to the chemical weapons convention would have had a much harder time making that convention if they thought that much (or all) of the U.S. implementation and enforcement would be left to each individual U.S. state without federal control, but I doubt it. In any event, if U.S. enforcement and implementation had been left to each individual state (i.e. without any federal implementing legislation), then perhaps the states could still be sued by the federal government for non-implementation.
The bottom line for me is that the federal implementing legislation is generally constitutional as being necessary and proper to carry into execution the executive power. Whether that legislation exceeds the scope of the treaty, or whether the treaty exceeds the scope of matters that are legitimately of international concern, or whether the treaty/legislation are ambiguous about the meaning of "chemical weapons" are matters that I now happily avoid.
Posted at 6:50 PM