WASHINGTON -- Vice President Joe Biden left the seclusion of the Delaware home where he's been weighing a presidential run to meet Saturday with Elizabeth Warren -- another influential Democrat who has faced calls to enter the 2016 race.

The unusual weekend huddle with Warren, a Massachusetts senator, took place at the Naval Observatory, the vice president's official residence, said an individual familiar with the meeting. An Obama administration official said Biden had traveled at the last minute to Washington for a private meeting and planned to return to Delaware the same day. Both of the individuals spoke on condition of anonymity because they weren't authorized to discuss the meeting publicly.

Biden's meeting with Warren was the latest sign that the vice president is seriously considering entering the race, and that he's increasingly discussing it with Democratic leaders outside of his small cadre of longtime advisers.

A rising star in the party, Warren was the subject of an intense lobbying campaign by a group called Draft Warren that sought to persuade her to enter the race. Warren ruled out running in 2016, and a super PAC similarly named Draft Biden later emerged and has been laying the groundwork for a potential Biden candidacy.

Warren, a vocal advocate for economic fairness and Wall Street reform, has notably refrained from endorsing Hillary Rodham Clinton, Sen. Bernie Sanders or the other candidates. She retains the vocal support of many in the liberal wing of the Democratic Party, making her endorsement one of the most highly sought in the primary.

Biden's quick trip to Washington wasn't on his official public schedule, which listed him as remaining in Delaware through Sunday. He's spent the past several days at his home in a secluded, wooded suburb of Wilmington spending time with family -- but also meeting with his longtime political aides to assess what it would take to launch a viable presidential campaign against well-funded Democratic opponents with a huge head start.

Spending time with Biden in Delaware has been longtime Biden confidantes Mike Donilon and former Sen. Ted Kaufman, along with his sister, Valerie Owens Biden, who has played a top role in all his previous campaigns. The Associated Press first reported on the Delaware meeting, while CNN first disclosed the session with Warren.

Although Biden has yet to make a decision, his advisers have started gaming out mechanics like fundraising, ballot deadlines and an early primary state strategy. Another key consideration is the personal consequences for Biden and his family, who are still mourning the death of the vice president's son, Beau Biden, a few months ago.

A look at the deliberations:

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TIMING

Biden's team has settled on a one-month window in September in which he could potentially announce plans to run.

The longer he waits, the less time he has to build a formidable campaign. But competing events on the administration's calendar make it difficult to launch in the next couple of weeks, making it more likely an announcement would wait until late September, aides said.

If Biden's not in by Oct. 1, it will be increasingly difficult for him to run, people who have spoken to Biden recently said. He'll need at least two full months to get the petition signatures and delegates lined up by the beginning of December to qualify for the ballot in early primary states.

Biden's aides are also eyeing the first Democratic primary debate -- on Oct. 13 -- as potentially a make-or-break moment. That first debate is expected to attract a huge audience among Democratic primary voters, giving Biden a powerful opportunity to establish himself as a credible alternative to Clinton.

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MONEY

Clinton and Sanders have already amassed millions of dollars while securing support from many of the party's top fundraisers.

With that reality in mind, his political advisers have discussed $5 million in hard money -- direct campaign contributions -- as a bare minimum of what they'd likely need in the first two months to open campaign offices and compete in the first primary contests. Separately, Draft Biden has set a goal to raise $2.5 million to $3 million in the next six or so weeks.

As a super PAC, Draft Biden is exempt from contribution limits, and could pay for pro-Biden television advertising. But the trappings of his current job make campaigning extremely expensive for Biden. When the vice president travels for political events, his campaign has to reimburse the government for much of the cost of Air Force Two.

It remains to be seen whether Biden could attract enough major donors and bundlers to fund a competitive campaign. After all, many of the party's top fundraisers are already committed to Clinton.

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THE MAP

Aiming to prove Biden would be competitive in key primary states, Draft Biden has been organizing and recruiting Democratic talent in Iowa, New Hampshire and South Carolina. This week Steve Schale, who ran Obama's presidential campaign in Florida, joined the super PAC, becoming the most senior Obama campaign staffer to publicly support a Biden run.

Biden's team has said it's optimistic about South Carolina, which holds the third primary contest and where Biden has deep political roots. Aiming to lock up support there, Clinton's campaign has dispatched top advisers John Podesta and James Carville to campaign for her in South Carolina.

In a bout of encouraging news for Biden this week, a Quinnipiac University poll of three battleground states -- Florida, Ohio and Pennsylvania -- found Biden faring as well as or better than Clinton against the top Republican candidates. In Ohio, 48 percent said they'd support Biden over Republican Donald Trump, giving Biden a 10-point lead over the GOP front-runner.