I have to caveat this with the fact that despite being a native New Yorker, I have never met Donald Trump, but have known people who have - mostly representing people in legal proceedings against him, although admittedly in his pre-frontal lobe dissolution days. And their assessment is that he's exactly as he appears, but with an almost incredible sense of self-preservation.
That said, I would suspect that it's exactly the fact that he is a ginormous, narcissistic, cunting, immoral arsehole pos that enables him to be charming enough from time to time to manipulate people when it suits him. And especially people with inflated senses of self, like Bill Maher.