I agree with Matt and just as a general rule – political or not – mental health professionals aren’t supposed to diagnose people without actually evaluating them. There are even some disorders where it’s recommended to see a patient for a minimum of 6 months to 1 year prior to diagnosis.
I think this LA Times Op-Ed does the best at evaluating his mental state against the most objective scale, the US Army Field Manual (but any evaluation is still subjective).
As a counter-point, while many mental illness could probably be ascribed to Trump – the most common is narcissistic personality disorder (NPD). However, the guy who wrote the criteria for NPD for the DSM-III and the same version is still used today does not agree with this. Specifically, because:
”Having the symptoms themselves does not constitute a mental disorder. In order to qualify as a mental disorder, the individual would have to have distress related to them.”
In related topics, here is a good article where they break down and studied his speech patterns over the years (ultimately, questioning his cognitive abilities). There was a Trumpcast episode with the author that’s a good conversation about it (link).
(Don’t get me wrong – I don’t think he’s mentally stable at all, but in a world where facts are still up for question by some, I think it’s important to be very precise in that realm).