Major Democratic fundraisers have been invited to meet with Vice President Joe Biden at his residence at the U.S. Naval Observatory after Labor Day, part of a series of conversations he is having with senior party players as he contemplates jumping into the 2016 race.

Among the guests invited to the gathering are top bundlers who raised large sums for the Obama-Biden campaigns in 2008 and 2012, according to people familiar with the outreach. The sitdown is scheduled to take place during the week following Labor Day.

Biden's office declined to comment.

In recent weeks, Biden has been huddling with longtime supporters and allies to discuss the possibility of making another White House run. On Saturday, he met with Elizabeth Warren, the populist senator from Massachusetts.

His consideration of another campaign comes as front-runner Hillary Rodham Clinton has fielded mounting questions about her use of a private email server while she was secretary of state.

The news that the FBI is investigating whether the system put any classified information at risk has rattled some top party financiers, particularly donors who were major players in Obama's fundraising network who have little personal history with the Clintons. In the last few weeks, e-mails and calls have been flying back and forth between top bundlers as they try to assess how serious Biden is and whether Clinton is on shaky ground.

"The network is starting to reach out," said one major Obama fundraiser, who requested anonymity to discuss private conversations. "I’m getting calls from people saying, 'We’re waiting for him to announce.' People are nervous and weary of the Hillary side show, of the emails."

Still, while there is deep affection and admiration for Biden, donors said many remain skeptical whether the 72-year-old vice president could mount the kind of operation needed to take on Clinton and then win a general election contest.

Many top Obama backers are now strongly committed to Clinton, and said they would remain so even if Biden jumped in.

Andy Spahn, a major Hollywood fundraiser who advises Jeffrey Katzenberg and Steven Spielberg, wrote in an e-mail that he has "much respect for the job Joe Biden has done as VP but it's too late in the game to mount a credible campaign. Hope he will join us all in support of Hillary Clinton's candidacy."

Biden's advisers have said that he will make a decision by the end of September.

Paul Kane contributed to this report.