I’m pretty sure that any medical professional who renders a diagnosis of Trump (or anyone) without actually examining them, is putting their medical license in jeopardy. Or at least opening themselves to an expensive lawsuit.
Yes, the article actually mentions that almost immediately, in regards to a lawsuit by Barry Goldwater for similar reasons. But then dismisses it, as Trump seems to be fair game to secular humanists.
A therapist in the story also questions the sanity of people supporting Trump, as he contends that they fail to grasp that with his ego he is unsuitable to be President. As I wrote above, the public is used to the egos of politicians, even though typically they try to cover up their ulterior motives and sell themselves as patriots and “public servants” of high ideals and virtues.
Trump has narcissistic qualities, as do many successful high energy persons, but does not come close to the boundary of a disorder. To say he has narcissistic qualities thus is not a diagnosis and probably protected speech.
(NB I have experience in forensic evaluations but am not a lawyer.)