The president pardoned a war criminal who stabbed a captive while he was being given medical aid by American medics and took a selfie which he then sent to his friends saying "Good story behind this, got him with my hunting knife". This is an exemplary soldier in the eyes of the American president. The fact that his administration wouldn't give a shit about prosecuting war crimes they are involved in doesn't surprise anybody.
They don't prosecute them as war criminals by building a case against themselves, but they will still prosecute individual soldiers when they feel like it, e.g. Graner and England for Abu Ghraib, but obviously not for war crimes.
We might be able to trust countries to judge their soldiers' behavior when these soldiers act on their own. The problem, and the reason, I believe, why the US won't voluntarily accept the ICC is when they don't, e.g. when drone operators bomb a wedding reception, because it's not going to be those individual operators on the hook - it's the mission and the larger policy that are going to be implicated. And a military doesn't want their officers to ask themselves "wait, can I do this? Will I be prosecuted for this?" when told to do something, they want them to say "Sir, yes, Sir" and mean it.