Dude, I knew he was a narcissist long before he even ran for president, and I consider numerous sources for news, taking each with a grain of salt. Honesty, just Google DSM criteria for narcissism, read it objectively, and tell me he is not a textbook case.
Here's where the media gets it wrong. Pathological narcissism is a personality disorder. It means you have a distorted view of yourself and the world around you which makes it difficult for you to develop proper relationships.
It doesn't mean you're insane. That's a legal term dealing with understanding of right and wrong. It doesn't mean you're psychotic.
While narcissists can be sociopaths, it's not part of the definition and it's not something I think fits Trump. Trump also isn't demented. He doesn't appear stupid, though he says a lot of things that aren't well thought out and come off as stupid.
Fact is that many people with personality disorders are able to function just fine in society, some quite successfully. These are extreme manifestations of clusters of personality traits held by many well-adjusted individuals.