International treaties are not automatically binding on the US. In US courts, they are binding only to the extent that Congress passes implementing legislation or Congress signals that it is self-implementing. But they have the status of ordinary law, so if the AUMF says the President can do something, as the later enactment it overrides anything in the Geneva Convention.
Outside of US courts international law is irrelevant as applied to the US. We're not a party to the ICC and we have veto power over any enforcement decision of the ICJ.
> We're not a party to the ICC and we have veto power over any enforcement decision of the ICJ.
We're getting a bit into the woods here, but veto power over the enforcement of UN rulings _does_ _not_ change international law. You can say that it is irrelevant because it is unenforceable, but _it_ _is_ _not_ legal for the U.S. to violate international treaties which it has signed. This is "legally binding". This is what that means.
The U.S. can overrule any enforcement decision, as you said. It cannot determine the ruling in any ICJ case.
Its a "what's the sound of one hand clapping" situation. We purposefully have not put ourselves in a place where international law cannot be enforced against us. Without that, its a total fiction to say there is any law. Unenforceable obligations aren't law. They're conventions or guidelines, maybe aspirations.
Outside of US courts international law is irrelevant as applied to the US. We're not a party to the ICC and we have veto power over any enforcement decision of the ICJ.