Joe Biden, who served as Barack Obama’s vice-president, believes he could have beaten Donald Trump in last year’s election if he had decided to run.
Mr Biden, 74, opted not to stand after his son Beau died in 2015 disappointing supporters who believed his folksy, blue-collar appeal would have been more than a match for Mr Trump’s populist campaign.
Some Democrats are still coming to terms with Hillary Clinton’s shock defeat and wondering whether they picked the right candidate.
Appearing before students at Colgate University in central New York on Friday, Mr Biden was asked whether he had any regrets.
“The answer is that I had planned on running for president. And although it would have been a very difficult primary, I think I could have won,” he said, according to the Observer Dispatch of Utica.
He added that he had collected a lot of data that indicated he could have been successful.
Mr Biden, 74, ruled himself out of a White House run in October 2015. He had emerged as a potential third way between Bernie Sanders’ on the Left and Mrs Clinton, who was criticised for her ties to Wall Street and a lingering row over a private email server when she was Secretary of State.
He had run twice before in 1988 and 2008, and had become a popular figure in Mr Obama’s administration.
But he said the “grieving process” for his son Beau, who died of brain cancer five months earlier, made it too difficult.
It was still the right decision, he told his audience.
"I didn't run because no man or woman should announce they're running for president of the United States unless they can look the public in the eye and promise you they can give you 100 percent," he said.
But that does not mean he is without regrets.
“At the end of the day, I just couldn’t do it. So I don’t regret not running,” he said. “Do I regret not being president? Yes.”