By Jeff Mason
EDGARTOWN, Mass. (Reuters) - U.S. Vice President Joe Biden met on Saturday with Senator Elizabeth Warren, a popular progressive leader with a big support base among Democrats, as he mulls whether to run for president, according to a source familiar with the matter.
Biden has been huddling with senior advisers to evaluate options for taking on former Secretary of State Hillary Clinton, the Democratic front-runner who has struggled to overcome fallout from her use of a private email server while working as the nation's top diplomat.
His meeting with Warren is further evidence of how seriously the vice president is considering a run for the party's nomination. Warren has a lot of support from liberal-leaning groups that would be critical to winning in early voting states.
She has said she does not plan to run for president herself, but she has not endorsed Clinton or any other Democratic candidate.
The vice president's office declined to comment other than to say Biden had left his home in Delaware to come to Washington.
"The vice president traveled last minute to Washington, DC, for a private meeting and will be returning to Delaware," a White House official said.
Biden's entry into the race would up-end the primary process. He has a long history of supporting policies to boost the middle class, an issue that is important to Warren and that Clinton has made one of the signature issues of her campaign.
But his late entry into the race and Clinton's formidable lead in infrastructure and fundraising would put him at a disadvantage.
"He has a resume second to none. He's been an extraordinary partner to this president. And economic viability of the middle class has been his focus and concern throughout his career," said David Axelrod, Obama's chief strategist in his 2008 and 2012 campaigns.
"That said, he's well behind the front-runner in polling, money and organization ... Unless the picture changes dramatically, it would be a heavy lift."
Though the vice president does not have a formal campaign structure, an outside political "Super Pac" called Draft Biden is laying the groundwork if he decides to jump into the race.
"All of a sudden the vice president's exceptionally serious," said Draft Biden adviser Steve Schale, a top strategist in Florida for Obama's campaigns in 2008 and 2012.
"Our job is to make sure that if he makes the decision to run ... there's a little bit of infrastructure in place for him to hit the ground."