Watch Barack Obama Fill in for Stephen Colbert

Outgoing host and leader of the free world also discuss Keystone pipeline, weak midterm election voter turnout in interview

With The Colbert Report inching toward its final episode on December 18th as Stephen Colbert readies taking over for David Letterman on The Late Show, the host welcomed "the leader of the free world and the new permanent host of The Colbert Report" President Barack Obama to the program.

Given the magnitude of his guest and Washington, D.C. episode location, Colbert lets Obama deliver the show's trademark "The Word" monologue. "Stephen, you've been taking a lot of shots at my job, I decided I'm going to go ahead and take a shot at yours," Obama said. From there, Obama pokes fun at his own health care bill. "Remember the original healthcare.gov website? I think that's where Disney got the idea for Frozen," the President jokes.

In their interview together, Obama and Colbert talk about the lack of voting among young people in the midterm elections, job creation and the Keystone XL pipeline. On that last topic, Colbert interrogates Obama whether he'll sign a bill approving the controversial pipeline that his audience vocally disapproves of.

"If we look at this objectively, we have to make sure it's not adding to the problem of carbon and climate change," Obama said. "Because these young people are going to have to live in a world where we already know temperatures are going up, and Keystone is a potential contributor to that." While Obama is critical of both the pipeline and the amount of jobs it would actually create in the U.S., he doesn't outright state he won't sign the bill when it inevitably reaches his desk.

In the second half of the interview, Colbert and Obama discuss whether the role of the president has "invested the executive with too much power." Colbert also jokes, "You have the nuclear launch codes, right? I'm not going to ask for them but is there a '5' in there?" The host wrapped up his Q&A with Obama by asking, "Barack Obama: Great President, or the Greatest President?" Obama replies, "I'll leave that alone, Stephen."