David Letterman may be retired but his opinion about Donald Trump still carries a lot of weight, especially when you consider that he has interviewed him many times over the years.In an interview with the New York Times, the legendary comedian who formerly hosted The Late Show talked about the Republican nominee and how the two used to interact on the program whenever Trump was a guest. Nobody took him seriously, and people loved him when he would come on the show,  Letterman said.  I would make fun of his hair, I would call him a slumlord, I would make fun of his ties   and he could just take a punch like nothing. He was the perfect guest. That s a complete flip from the Trump the public has seen over the last year and a half. Trump is known for having a thin skin and he often lashes out over the smallest slights against him. Just a simple criticism is enough to send him over the edge, whether it s on Twitter or during his rallies.It was during one such rally when Trump attacked a reporter critical of his campaign by mocking his disability on stage in one of the most disgraceful moments of the 2016 Election season.And it s a moment Letterman says should have disqualified Trump and made him a pariah in our society. I can remember him doing an impression, behind a podium, of a reporter for the New York Times who has a congenital disorder, and then I thought, if this was somebody else   if this was a member of your family or a next-door neighbor, a guy at work   you would immediately distance yourself from that person. And that s what I thought would happen. Because if you can do that in a national forum, that says to me that you are a damaged human being. If you can do that, and not apologize, you re a person to be shunned. Letterman then suggested that Trump is behaving so badly that he should get his head examined. I don t know anything about politics. I don t know anything about trade agreements. I don t know anything about China devaluing the yuan. But if you see somebody who s not behaving like any other human you ve known, that means something. They need an appointment with a psychiatrist. They need a diagnosis and they need a prescription. Indeed, Trump s mental health has been a great concern to many people. Even Dr. Drew and board-certified psychiatrist and Fox pundit Charles Krauthammer have weighed in on the subject.But regardless of why Trump is acting the way he is, the point is that it is far from presidential and should disqualify him from ever holding the office. America does not need a president who is easily provoked, especially when he will have the nuclear codes. We need a president who is good at working with others and has a calm steady hand. That person is not Donald Trump.Featured image via Salon