In a moving interview with comedian Stephen Colbert that aired late Thursday night, Vice President Joe Biden suggested he is not yet emotionally prepared to run for president in 2016, as he is still reeling from the death of his son earlier this summer.

“I don’t think any man or woman should run for president unless, number one, they know exactly why they would want to be president and, number two, they can look at folks out there and say, ‘I promise you, you have my whole heart, my whole soul, my energy, and my passion to do this,’” Biden told Colbert, who recently took the helm of on CBS’ “The Late Show” from longtime host David Letterman.

“And I’d be lying if I said that I knew I was there,” Biden continued, according to a pool report.

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Biden, who has run for president twice, has been taking a closer-than-expected look at a 2016 presidential bid against front-runner Hillary Clinton, whose poll numbers have slumped under the weight of controversy over the private email server she used as secretary of state. The vice president has been calling allies and Democratic donors as he feels out a bid.

But Biden has also said he and his family may not be up to the challenge in light of the death of his son, Beau, from cancer in late May. Aides to the vice president say his feelings and grieving vary day to day.

Close video The ties that bind the Biden family The Biden family gave their beloved son, brother, husband and father, Beau Biden, an incredibly personal goodbye Saturday. Bill Scher, Jessica Taylor and Robert George discuss. The Biden family gave their beloved son, brother, husband and father, Beau Biden, an incredibly personal goodbye Saturday. Bill Scher, Jessica Taylor and Robert George discuss. share tweet email Embed

Biden told Colbert that “nobody has a right in my view to seek [the presidency] unless they’re willing to give it 110%.”

“And I am — as I said I’m optimistic, I’m positive about where we’re going,” Biden continued. “But I find myself — you understand it — sometimes it just overwhelms you.”

The vice president went on to recount a recent visit to a military base in Denver where he met a group of military families. “And all of a sudden — it’s going great — and a guy in the back yells ‘Major Beau Biden, bronze star, sir, served with him in Iraq.’ And all of a sudden I lost it,” Biden said. “How could you … I shouldn’t be saying this — you can’t do that.”

Biden spoke emotionally of his son, telling a story of a conversation they had before Beau died. “He said, ‘Dad, sit down, I want to talk to you,’” Biden recounted. “And he said, ‘Dad, I know how much you love me. You’ve got to promise me something. Promise me you’re going to be alright. He said no matter what happens dad, I’m going to be all right. Promise me.’ This is the kid who — I don’t know what it was about him. He had this enormous sense of empathy.”

And Biden, who as a young man lost his wife and daughter to a car accident, spoke about how his religion has been an “enormous sense of solace” during his suffering how his family has supported him. “First of all it’s a little embarrassing to make this about me. There are so many people — even in the audience — who have had losses as severe, or worse than mine and didn’t have the incredible support I had. I have an incredible family. And I feel so self-conscious. The loss is serious, it’s consequential, but there’s so many other people going through this,” he said.

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Colbert shared a bit about his own childhood, which included the death of his father and two brothers in a plane crash. “It’s going to be emotional for a lot of people if you don’t run,” the host told Biden. “And sir, I just want to say I think your experience and your example of suffering and service is something that would be sorely missed in the race. Not that there aren’t good people on both sides running. But I think we’d all be very happy if you did run. And if you don’t, I know that your service to the country is something we should all salute. So thank you so much.”

The interview, which was recorded earlier Thursday evening in the Ed Sullivan Theater in midtown Manhattan, will air later during Colbert’s third episode as host of “The Late Show.”