Cassandra has a good, detailed post that explores the hypothetical primacy of international law over domestic law. There’s not much I can add to her post, other than I agree with her and hope that, when the time comes (if ever), it is approached by amending the Constitution, not imposed on us by our robed masters. It would take several decades of goodwill on the part of the rest of the world before I favored this. Even then, I would wait until right before death to say it out loud, so I don’t have to deal with the aftermath.
Cass’s post is a followup to an earlier post of mine. Be sure to wish her well as she takes a little time off from blogging. You’ll have to use a different post for that, as she’s closed comments on the linked post.