Honestly, even before Trump came along US credibility was on shaky ground. We hadn't forgotten Iraq, for example. It was just good enough for the most part - you could make a deal with the US and usually expect them to mostly adhere to it as long as it was in their interests.
Now you can't even expect them to do what's in their own best interests any more, and the concept of them "sticking to a deal" a moment longer than the point where breaking it gets them an atom of short-term benefit is gone.