The frequent about-faces and erratic pronouncements of Trump are enough to discourage anyone from engaging in diplomacy with him, much less a proud country like Iran that feels the US has repeatedly intervened in its affairs, even to the point of overthrowing its government in 1953.
Trump is stuck.
Worse, we're stuck with Trump at the helm of the foreign policy of the world's sole superpower. He actually casually talked about war with Iran. God help us.