Escalation seems inevitable. Iran's leaders can't be deterred by threats of destruction.

In their eyes they are God's anointed representatives on Earth. The God they think they serve embraces vengeance as much as mercy, and martyrdom more than happiness and life itself. In the name of God they have slaughtered tens of thousands of their own citizens, in order to maintain their grip on power. They virtually care nothing whether the U.S. kills thousands more innocent Iranians. Martyrdom, they believe, will reward the innocent in the afterlife to come.

They have no absolutely no trust in negotiations with America. Twice already the U.S. unleashed military force against Iran literally while negotiations were ongoing. Israel and America are actively targeting them for assassination already. What more do they have to lose? There is no good faith basis for negotiations, only power (and of course God's Will) can prevail, and there is no power in surrender, only in resistance. If they agree to lessen the pain Americans, and the greater world must endure, they have no means left with which to resist. To Iran's leadership it must seem more likely that the American people, once their economic suffering becomes intolerable, will depose our current leadership than that the Iranian public will depose their theocratic regime which Allah, they believe, has blessed. The suffering of their own people will no more deter Iran's current leaders than the suffering of the people of Gaza deterred Hamas. But unlike Hamas, Iran's mullahs have identified the means needed to deliver mass suffering onto their foes and on those they believe to be complicit in the war against Iran. Why, in the name of God, would they hesitate to use it? Unlike Trump, they have nothing to conceivably gain by bluffing.