I have one word that covers what Trump has done: "insane".
It ramps up greater risks of war, plus if Iran were to return to being able to make nukes, then the Saudi's, and possibly some others in the region, may also decide to do the same.
But what's also terribly important is that it tells all, including our allies, that this administration cannot be trusted to apply any agreement that we may have signed or may sign in the future. Like with marriage, trust is important, and the only thing we can trust with Trump is that he simply cannot be trusted.