I think you are correct, he had a deal with one side and the other took over negating it. We apparently did not understand where the power was in their system of government. We were over reliant on the belief the civil side would win out over the Islamic nut jobs.
We began trying to ensure their nuke program was kaput and are now arguing over the free movement of shipping through the Straits. Trump is trying to negotiate his way out of the war and that is not going as we hoped. Worse, we got the backstabbing media and dems undermining our position.
I don’t have most all of the info the president has so it would be foolish for me to speculate. From the uninformed point of view, I’d say be careful in any talks with nut case zealots, their end point is not the same as ours. Recall the Japs had thousands of zealots who would crash a plane with a bomb into a ship fully knowing the war was lost.
The Trump admin assumption was, apprently, that taking the leadership out would cause a popular uprising by the Iranian people. When that didn’t happen there was no Plan B because to do it by military force would be a massive and historical operation. There simply isn’t the political will to get that done now for reasons of your chosing.