U.S. Vice President Joe Biden expressed uncertainty about the prospect of a 2016 bid for the White House Thursday night, telling an audience at an Atlanta synagogue: “I can’t look you straight in the eye and say now, ‘I know I can do it.’”

Addressing recent speculation that he was preparing to launch a bid for the presidency, Biden, who unsuccessfully sought the Democratic nomination in both 1988 and 2008, told reporters that his family's well being would be the key factor in his decision on whether to run or not.

The 72-year-old vice president said he was still gauging his family's "emotional energy" to join the race, calling it "the most relevant factor" in his decision-making process, CNN reported. Biden's eldest son, Beau, died as a result of brain cancer in May, aged 46.

"Unless I can go to my party and the American people and say that I'm able to devote my whole heart and my whole soul to this endeavor, it would not be appropriate," Biden said. "And everybody talks about a lot of other factors: The other people in the race and whether I can raise the money and whether I can get an organization. That's not the factor. The factor is can I do it? Can my family?"

Speculation about a possible Biden run has been growing in recent weeks, as Democratic frontrunner Hillary Clinton has seen her support in polls drop sharply, after her use of a private email server while she served as secretary of state became the subject of controversy.

Biden prompted further speculation about his intentions last month, after meeting privately with Sen. Elizabeth Warren (D-Mass.), who is highly popular with the Democratic base, but is not running in 2016.

Aides told the New York Times that Biden may not decide until early October or perhaps later, though on Thursday, Biden said: "There's no way to put a timetable on this."