I’m delighted to see Rick Pildes will be guest-blogging, and the exchange with Nick on the Treaty Power will be a treat.
I would invited them to consider an aspect of the question that has long interested me:
What is the relationship between the Offenses Power, the Treaty Power, and the Foreign Commerce power? All three might overlap at their edges (assuming they are not entirely congruent), and the extent of the overlap would say a lot about the extent of the other powers. If for example, the Foreign Commerce power is even broader than the Interstate one, then the scope of the treaty power becomes even less important.
Hamilton, as I’ve mentioned before saw the Treaty Power as in some ways ways being not coterminous with the Foreign Commerce power, and my understanding of the Offenses Power has always been that it was distinct from the Treaty Power. An example of how such delimitations might matter would be whether the courts can consider, as they sometimes do, unratified treaties in determining the “Law of Nations.”
UPDATED with minor edits.