The White House staff routinely used a process of delaying any time he made some hair-brained request. He generally forgot, or some other shiny object caught his eye. Otherwise they would have to talk him out of it (very persuasively and flattering about it).

You may have to click past a paywall or a cookie query, but this Vox article about the "Goldwater Rule" is interesting. This is extracted from the 2017 piece:

Fact magazine called this “the most intensive character analysis ever made of a living human being.” What it was: a complete embarrassment to the field of psychiatry and the beginning of the end for Fact. After his election loss, Goldwater successfully sued the magazine for libel; the $75,000 settlement put the small publication out of business.

And the episode compelled the APA’s ethics committee to ban its members from making future diagnoses about public figures in the press.

It only applies to card-carrying APA psychiatrists. It doesn’t apply to psychologists, social workers, or New York Times columnist David Brooks. In February, a psychologist told me with deadly seriousness, “This is the worst case I have seen in my career,” regarding Trump and a diagnosis of narcissistic personality disorder.

So while claims about the president’s mental health have been made by just about every other group of person on earth, psychiatrists are discouraged from jumping in, even to correct the record.

Trump's niece is a psychologist, so isn't bound by this restriction in sharing her observations about her uncle Donald.

There's a short video that pops up on Instagram occasionally with a few well-regarded psychiatrists and psychoanalysts who have decided to disregard the Goldwater Rule for the protection of the country and pronounce Trump unfit. If I see it again I'll grab a link and share it.