I think Donald J. Trump is plenty bright. Not in the intellectual, Mensa-meeting sense, but he has, I think, an undeniable intelligence. He is street smart, savvy, clever. No one can be that conniving and be an idiot.
So why the disconnect? Why do I as an outside analyst see an intelligence that those closest to the President do not? Because there are different kinds of intelligence that are useful for different purposes. The kind of intelligence I believe Trump has is enormously useful if you want to, say, be a politician -- even better if you want to be a demagogue.
(The piece is a bit dated, but really quite insightful.)