Political scientist Brendan Nyhan notices that psychiatrist and political commentator Charles Krauthammer has both criticized and engaged in long-distance diagnosis of public figures. Nyhan wonders if there is a professional misconduct policy that might be relevant.
There is. See Principles of Medical Ethics with annotations applicable to psychiatry, Section 7: Paragraph 3:
On occasion psychiatrists are asked for an opinion about an individual who is in the light of public attention or who has disclosed information about himself/herself through the public media. In such circumstances, a psychiatrist may share with the public his or her expertise about psychiatric issues in general. However, it is unethical for a psychiatrist to offer a professional opinion unless he or she has conducted an examination and has been granted proper authorization for such a statement.
But I don't think Dr. Krauthammer has anything to worry about. See my comment.
I must admit that I do experience the urge to offer diagnostic impressions of public figures from time to time. But more often, I feel compelled to comment on faulty diagnoses offered by lay persons, as I did in this post and in this post. I also find myself mildly annoyed with amateur estimates of IQ. There's a lot of that going around.