Or maybe ...
... Erich Fromm was a psychiatrist in the United States who immigrated from Hitler's Germany in the 1930s. He was a world leader in many aspects of mental health and diagnosis. ...
Fromm said that benign narcissism focuses on pride in one's work, one's effort. In the process of achieving something, the person has to stay in touch with the reality around the task in order to accomplish it. "The energy which propels the work is, to a large extent, of a narcissistic nature, but the very fact that the work itself makes it necessary to be related to reality, constantly curbs the narcissism and keeps it within bounds. This mechanism may explain why we find so many narcissistic people who are at the same time highly creative."3
On the other hand, there is a malignant narcissism. This is not about achievement, but rather something the person thinks they inherently have that's special, "for instance, his body, his looks, his health, his wealth, etc. ... Malignant narcissism, thus, is not self-limiting."4 ...
The essence -- and biggest danger -- of malignant narcissism is that it keeps growing, like malignant cancer.
Fromm wrote: "It is a madness that tends to grow in the lifetime of the afflicted person. The more he tries to be a god, the more he isolates himself from the human race; this isolation makes him more frightened, everybody becomes his enemy, and in order to stand the resulting fright he has to increase his power, his ruthlessness, and his narcissism."6
Does This Fit President Trump?
Some mental health experts say "Yes;" some say "No;" and many say they can't say because they have never done a clinical interview with him and so it would be unprofessional to state an opinion about his mental health.
As a Licensed Clinical Social Worker, I am in the third group, so I will not be saying whether he meets this diagnosis or not. But I am clear that he has a high-conflict personality, which is a description of conflict behavior -- extremely concerning conflict behavior -- but not a mental health diagnosis. (See my other posts here for more on high-conflict personalities.) ...
Horde.
It's too early for historical accuracy.