"I'm not closing the door. I've been around too long," Biden said on NBC's "Today" Monday morning as part of a publicity tour for his new book
, "Promise Me, Dad: A Year of Hope, Hardship, and Purpose."
"I'm a great respecter of fate ... but who knows what the situation is going to be a year and a half from now. I don't have any idea. I'm in good health now. I'm in good shape, knock on wood, as my mother would say. But I just, I don't know."
The former vice president will be 75 years old this month, making him almost four years President Donald Trump's senior. In an interview with Oprah Winfrey that aired Sunday, he pointed to his age as a reason for his uncertainty.
"I'm -- thank God right now -- in awful good health," Biden said. "But I don't know what the things are going to be two years from now."
Biden flirted with a presidential bid in the last election cycle, and his forthcoming memoir chronicles the year 2015, in which his son, Beau, died of brain cancer at age 46, and he decided against running in the presidential race out of concern for his family and the need to grieve for Beau's loss.
In the interview with Winfrey, Biden said he made the right call, but he repeated his regret that he had not ascended to the nation's highest office.
"I have a regret that I am not president," Biden said. "But I don't regret the decision I made because it's the right decision for my family."
Asked if he thinks he could have defeated Trump in the 2016 presidential contest, Biden told "Today" he wasn't sure.
"Oh gosh, I don't know. I mean, the polling data at the time said yes, and since then. But ... I wasn't in the race. You have to be in the race. It's a tough game," he said.
Biden contended that while he thought he could have secured the Democratic nomination, he also thought Hillary Clinton would be a great president.
But, he said, as Election Day approached, he thought Clinton would lose.
"I did 83 events," Biden told Winfrey. "A month out, I came back and said, 'We're going to lose this election.'"
Biden said the presidential campaign was not dedicated enough to talking about the issues, citing studies showing how little policy came up and asserting that candidates have to stake out affirmative positions.
"I'll bet you can't find 10 friends who could tell you what Hillary's position was on child care," Biden said. "Not generically, specifically. How we're going to have free college education, how it's going to be paid for. All the things that matter to those people."
Biden also pinned Clinton's loss in part on "identity politics" and bemoaned her campaign's inability to follow in the footsteps of former President Barack Obama's successful presidential bids.
"I think what happened is we got to the point where it became identity politics," Biden said. "They learned the wrong lessons from Barack's brilliant campaigns."