I've always found claims that Trump is the worst president in US history to be premature and silly. I can think of several far worse presidents than Trump.
But I think it is fair to ask if Trump is perhaps the dumbest president in US history. Keep in mind, I'm not saying Trump completely lacks intelligence. Clearly he understands how to deal with people, which is a form of social intelligence. But the same thing can be said about Kim Kardashian.
What I'm really asking is this: Is Trump perhaps the least knowledgeable and astute president in US history? Does Trump actually THINK about anything he does? Or does he just operate on pure emotion and instinct? I think one look at his Twitter history should answer that question.