Yes, most people are rather slow on the uptake. I've already known he was dumb from at least as early as the 1980s.
Actually in his interviews from the 80's he seemed to be fairly intelligent and well spoken, for a guy like that. That couldn't be really said now, you can just compare and look at the way he speaks. Too much narcissism combined with possible dementia shows, probably the junk food that he eats isn't helping with the way his mind is functioning.