REUTERS/Joe Skipper
Vice President Joe Biden.
Biden, taking questions after giving a foreign-policy address in Atlanta, Georgia, said he simply wasn't sure whether he was ready for the rigors of the campaign trail.
He said the only factor in his decision-making process was how his family was coping with sudden absence of his late son, Beau Biden, who died earlier this year after battling brain cancer.
"I will be straightforward with you. The most relevant factor in my decision is whether my family and I have the emotional energy to run," Biden said.
"Some might think that is not appropriate," he added. "But unless I can go to my party and the American people and say that I am able to devote my whole heart and my whole soul to this endeavor, it would not be appropriate."
Biden is widely viewed as one of the only remaining Democrats who can still enter the presidential fray and present a notable primary challenge to former Secretary of State Hillary Clinton.
Clinton, the party's front-runner, has had a particularly rough summer amid questions over the private email server she exclusively used for her State Department business. Critics claim she violated protocol and jeopardized classified information. Clinton's allies dismiss those claims as unfounded partisan attacks.
Polls show Biden would enter the race with a steep hill to climb against Clinton, who has had months to build a massive fundraising network and campaign infrastructure. But Biden dismissed those potential obstacles during his Thursday address.
"And everybody talks about a lot of other factors: the other people in the race, whether I can raise money, and whether I can put together an organization. That's not the factor," he said. "The factor is: Can I do it? Can my family undertake what is an arduous commitment that we'd be proud to undertake in ordinary circumstances? But the honest to God answer is I just don't know."
Biden reminded his audience that he is no stranger to tragedy - his wife and one-year-old daughter died in a car accident after he was first elected to the Senate in 1972 - and he knows he cannot put a "timetable" on the 2016 question.
"If I can reach that conclusion that we can do it in a fashion that would still make it viable, I would not hesitate to do it," he said. "But I have to be honest with you and everyone who's come to me: I can't look you straight in the eye and say now, 'I know I can do that.' This is as honest as I can be."
Watch below, video via CNN: