he's a textbook narcissist and everyone has known that since well before he got elected the first time.
the "interesting case" is how he somehow managed to convince the average american that he has anything in common with them, even as he insulted everything they stand for, constantly. there is the real psychological case study.
> how he somehow managed to convince the average american
Unless you have dealt with a narcissist in real life you don't really get to comprehend the reality of them and their methods. On the other hand, once you know, most of them are so transparent.