David Letterman regularly cracks jokes on his "Late Show," but on Oct. 23 he turned very serious and talked on camera about how disappointed he is with President Barack Obama and Mitt Romney.

Talking to his guest, Rachel Maddow, he bashed the presidential candidates on Tuesday night for not giving enough attention to topics that are important for younger generations. One reference he made was to their lack of discussion regarding global warming.

"That bothers me, because I've got an 8-year-old son. What's the world going to be like when he's 65 years old?" Letterman said.  He also brought up the topic of gun control.

"Of course they're not going to talk about gun control because it's a hot button issue," he said. "Well, I'm interested in hearing what the future might be for my son... Substantively speaking, what will the world look like when I'm gone and my son's still here? I got no answers for that."

"I understand people who have guns. I understand people who hunt. I understand people who want to protect themselves. But I am sick and tired of mass shootings on college campuses and in theaters," he added.

Letterman had President Obama as a guest on his show in September. They both discussed Romney's "47 percent" comment regarding Obama's supporters. Romney himself has not been a guest yet on Letterman's show. However, earlier this month, Letterman made a comment on air basically stating that if Romney wants to win the election, he needs to make a stop on "The Late Show."

"You can't blow this off, Mitt. I'm telling you, with every fiber of my being: if you want to go to the White House -- not on the tour -- you have to come here and shut me up," Letterman said on camera. "You've gotta prove that I'm a dumbass punk and you've gotta come here and do it now... Because we wouldn't want anything to go the wrong way."

"The Late Show with David Letterman" airs weeknights on CBS at 11:35/10:35c.

Tags: David Letterman Barack Obama mitt romney