Current Presidential candidate Donald Trump and former late-night host David Letterman go way back. Trump appeared several times on both of Letterman's shows — first on Late Night, and then on the Late Show — and back then, when Trump was just an over-the-top New York businessman and not the potential next leader of the free world, he was a frequent target of Letterman's jabs, with the host making fun of Trump's clothes, his hair, and his business flops.

But in a new interview with the New York Times, Letterman says he no longer finds Trump to be a laughing matter. He cited the time Trump did a cruel impression of a New York Times reporter with a disability as something that should bar Trump from polite society, let alone the presidency.

"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," Letterman says of Trump's lack of civility. "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."

Donald Trump and David Letterman, <em>Late Night with David Letterman</em>Donald Trump and David Letterman, Late Night with David Letterman

Letterman says — probably truthfully, considering his track record of making celebrities uncomfortable, including Trump during a memorable 2012 appearance — that if candidate Trump appeared on his show, he wouldn't go easy on him the way other hosts, including Jimmy Fallon, have been accused of doing this election cycle.

"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?'" he says. The discussion wouldn't have been about politics, a topic Letterman claims to not know much about, and just about the basic human decency he feels Trump lacks.

Letterman retired from the Late Show in May 2015, just a few weeks before Trump began his campaign. The late night landscape is certainly lacking without his acerbic tone.