IF he did say that, is he not entitled to be mistaken about something once in a long while ? We can compare with all the things he said that turned out to be right, when Democrats had insisted the opposite, and they were wrong.
Also, What Trump often says, comes from his intelligence sources, so was he wrong, or were they ?
Lastly, maybe he was right. Maybe Iran's nuclear weapons capabilities had been completely and totally obliterated. And then maybe they then started from scratch, and rebuilt them again. I sense that when it comes it the US government, a lot of people talk without really knowing all the facts, in complex scenarios.