The comments came amid fevered speculation about a possible Biden candidacy -- chatter that he has stoked by meeting in recent weeks with key liberals, including Sen. Elizabeth Warren (D-Mass.) and Richard Trumka, the president of the AFL-CIO union as he decides what to do.
But close friends and associates say Biden is still reeling from the death of his 46-year-old son, Beau Biden, who passed away in May after a bout with brain cancer. In the wake of his death, news reports said that in his final months, the vice president's son had urged him to run for president.
On Thursday night, Biden articulated publicly what had been telegraphed privately by friends and aides: That family considerations remain his biggest obstacle to a possible candidacy.
“The most relevant factor in my decision is whether my family and I will have the emotional energy to run," he said. "Some might think that’s not appropriate. Unless I can go to my party and the American people and say I’m able to devote my whole heart and my whole soul to this endeavor, it would not be appropriate."
"Everybody talks about a lot of other factors," he added. "Other people in the race, whether I can raise money and whether I can put together an organization. That’s not the factor. 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. The honest to God answer is I just don’t know."
Biden said that after the death of his wife and daughter shortly after he won his Senate seat in 1972, "there's no way to put a timetable" on such a decision.
"If I can reach that conclusion and we can do it in a fashion that would still make it viable I would not hesitate to do it," he said.
His comments Thursday night echoed similar sentiments he shared with Democratic Party activists last week. During a conference call with leaders of the Democratic National Committee, he openly pondered whether he has "the emotional fuel" for a White House run, according to a CNN report on the call.
Biden's latest comments came amid a reemergence that began on Wednesday in Miami with a speech on community college education and an appearance at a long-scheduled fundraiser for Democratic senators.
He began the day on Thursday at a Jewish community center in Davie, Fla., where he spent about three hours meeting with supporters of Rep. Debbie Wasserman Schultz (D-Fla.) to explain and defend the nuclear deal. It was his most public and expansive review of the deal since it was brokered.
During the meeting, a brief reference to his deceased son prompted Biden to choke back tears.
As he continues mulling a run, Biden is set to attend to a mix of official and political duties. On Friday, he will join President Obama in separate meetings with Saudi leaders and Defense Secretary Ashton Carter. On Monday, he is set to march with Trumka in a Labor Day parade in Pittsburgh.