The ICC treaty says the ICC can only try people that cannot or will not be tried in their own countries. That is to say, accusations of war crimes would have to go before US courts first. The US opposes the ICC treaty because it has no intention of prosecuting war crimes at home. If it did, there would be no reason to worry about "politically motivated prosecutions" or anything like that, which are just propaganda talking points by opponents of international law.

A society committed to the notion that government is always bad will have bad government. And it doesn't have to be that way. — Paul Krugman