The US have stated that trying to have an international trial against a US citizen (for e.g. crimes against humanity) will result in use of military force. Do you really think anything is off limits for a government with that attitude? Remember this are laws the US recognizes and even was one of the parties who created them and enforced them (e.g. at the Nuremberg trials).
The US is rapidly becoming the biggest enemy of itself and no, while a superpower it can't simply ignore the opinions of the rest of the world.