If Donald Trump is good at one thing, it’s keeping his word on election promises. The promises may have been utterly crazy, but Trump does appear to be sincere about trying to deliver. Abandoning the 2015 Iran nuclear deal with the "strongest sanctions in history" is a key case in point.
Apart from a poorly informed campaign promise, there’s no logical reason why Trump has dumped the Iran nuclear deal. It was not, as he said, "insane" and he was incorrect to claim that the US has paid Iran hundreds of millions of dollars in cash to sustain the deal. The US instead lifted a blockade on Iranian bank accounts, which provided Iranians with access to billions of their own money.