I don't have any empirical evidence of his relative intelligence but I can say I have never, ever heard him speak eloquently or as an informed authority on any single matter he is talking about. This is going back to him in the 80's as a real estate guy working to bilk NYC out of tax $. Sure he has the tongue of a charlatan, but that is it, well maybe that he ranks among one of the most successful charlatans in career longevity and success but a charlatan nonetheless.
Even his career/monetary "success" is shrouded in his pathological lying. The only thing I know to be factual that he says is that he is the president and in true form he even takes that a step further with lying about how he got there.