My point is that the US could "assent to the validity of the ICC charges". The "fantasy" is several unlikely escalations away after that, and even that scenario is something that the US could deal with.
So ruling out that they go against the ICC because they have to, we can conclude that they go against the ICC because they want to.
Something like half the world's population doesn't acknowledge the ICC. And the ICC hasn't covered itself in glory over the last 20 years --- the Darfur fiasco being the most obvious example.
All this just brings me back to: the ICC charges are a political act (fair enough! politics matter!) and should be evaluated on their political effectiveness. The predictable result of the charges: the leader of the only political party in the US that even ostensibly cares about Palestine disavowed the charges. How'd that help?