Mr. Letterman, 69, had an especially feisty relationship with Donald J. Trump, who had been a frequent guest and sparring partner since the 1980s. As an interview subject since becoming the Republican presidential nominee, Mr. Trump has since bedeviled hosts like Jimmy Fallon (who was criticized for going too easy on him) and Stephen Colbert (who acknowledges he should have been a tougher interrogator). But Mr. Letterman seemed to land some lasting hits on Mr. Trump: a 2012 “Late Show” segment in which he mocked Mr. Trump for outsourcing his Macy’s clothing line to Asia resurfaced this year in a campaign ad for Mrs. Clinton.
Now Mr. Letterman says that Mr. Trump is no longer a laughing matter. In an interview on Wednesday to discuss his involvement in the National Geographic Channel series “Years of Living Dangerously,” which examines environmental problems around the world, Mr. Letterman spoke about his evolving thoughts on the Republican nominee and why he considers him “a damaged human being” and “a person to be shunned.” These are edited excerpts from that conversation.
Q. You featured Donald Trump on your programs many times over the years. What perspective has that given you on his presidential candidacy?
A. I’ve known Donald Trump for a long time and I always thought he was exactly what New York City needed to have: the big, blowhard billionaire. “By God, I’m Donald Trump and I date models and I put up buildings, and everything is gold.” Nobody took him seriously, and people loved him when he would come on the show. 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.
So now, he decides he’s running for president. And right out of the box, he goes after immigrants and how they’re drug dealers and they’re rapists. And everybody swallows hard. And they think, oh, well, somebody will take him aside and say, “Don, don’t do that.” But it didn’t happen. And then, 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.
I kept telling people he will absolutely not get elected. And then David Brooks said he’ll get the nomination and he will be crushed in the general election. And I thought: Yeah, that’s exactly what’s going to happen. I stand by that. The thing about Trumpy was, I think people just were amused enough about him to keep him afloat in the polls, because nobody wanted the circus to pull up and leave town.
How did you feel about the Clinton campaign using the “Late Show” video in an anti-Trump ad?
It made me a wealthy man. [laughs, then seriously] I was flattered. I was pleased. I felt like I still have a small voice in this. I thought it was good. Slowly but surely, everybody got sucked into this vortex. “Did you hear what Donald Trump said?” And everything downstream got worse and worse. Poor Ruth Bader Ginsburg gets sucked into it, and I’m thinking, Oh, don’t take the bait, ma’am. Then she says so-and-so and she has to apologize. Kids, if you turn off the light, the moths will stop coming.
Jimmy Fallon seemed to try a different approach, by not even addressing Trump’s controversies, and it got a negative reaction. How would you handle Trump as a guest now?
If I had a show, I would have gone right after him. I would have said something like, “Hey, nice to see you. Now, let me ask you: what gives you the right to make fun of a human who is less fortunate, physically, than you are?” And maybe that’s where it would have ended. Because 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.