Vice President Joe Biden told comedian Stephen Colbert he can’t yet say whether he’s ready for a run for the presidency.

“I'd be lying if I said that I knew I was there,” Biden told Colbert in an emotional interview that will air on CBS Thursday night. “I'm being completely honest. Nobody has a right in my view to seek that office unless they are willing to give it 110 percent of who they are."

The remarks came as Colbert asked Biden about addressing “the elephant in the room, which in this case is a donkey” -- or whether or not he’ll consider a run for the presidential nomination as some Democrats are hoping, given the email controversy dogging Hillary Clinton’s campaign.

But Biden, who talked with Colbert about the pain of losing his son, Beau to cancer this summer, suggested he may not be emotionally ready for a grueling presidential campaign.

“I'm optimistic. I'm positive about where we’re going,” he told Colbert. “But I find myself...you understand, sometimes it just sort of overwhelms you. I can't..."

He said no one should run for president “unless, number one, they know exactly why they would want to be president and two, they can look at folks out there and say I promise you have my whole heart, my whole soul, my energy, and my passion.”

Colbert, who was 10 when his father and two brothers were killed in an airplane crash, told Biden it would “be emotional for a lot of people if you don't run. Your example of suffering and service is something that would be sorely missed in the race."

Biden said he’s found the outpouring of support for his loss a “little embarrassing,” noting that “so many people who have losses as severe or maybe worse than mine and don't have the support I have."

There were moments of levity. Biden’s segment opened with a hitch when his microphone failed to work. As technicians worked on the microphone, Colbert, who started hosting the Late Show on Tuesday night, joked to the audience that it was there for his last show. “Almost made it to Friday," he said.

Quipped the gaffe-prone Biden, "by the way, they do this to me at the White House all the time. Shut my mic off."