Whilst agreeing with you in principle I just have in the back of my head the widespread scorn in which the U.N. is held by many people, including politicians, in the USA, who see it as being as useless as the League of Nations.
In the case you put forward I think it would end up as more of a case of the USA walking away rather than being pushed - and from the U.N. as a whole. it certainly won't stop them taking action - as they have made clear.