WASHINGTON (CNN) -- Vice President Joe Biden has yet to rule out a 2016 presidential campaign and is likely to wait beyond August to decide, several Democrats say, allowing him to watch as the contest unfolds before determining whether he could make a viable late entry into the race.

While Biden has done little to lay the groundwork for a possible challenge to Hillary Clinton and the rest of the Democratic field, CNN has learned that a group of his friends and advisers are still urging him to keep the door open. He has not discounted those arguments, Democrats close to him say, and he feels no pressure to reach a decision by the end of summer as he once suggested.

\"I know there are a lot of people around the country who would like to see him run and think he'd be a terrific president,\" said Sen. Tom Carper, a Delaware Democrat and longtime friend of the Biden family. \"They are biding their time and holding their fire until Joe is ready to make that decision.\"

With the Iowa caucuses and New Hampshire primary six months away, Biden is the leading figure Democrats believe they could turn to if they needed to find an alternative to Clinton, whose favorability ratings have taken a deep hit as her email use while secretary of state is still drawing controversy.

Helping the party

The prospects of Biden running, his advocates say, are rooted not only in his own ambitions, but also with an eye toward helping the party put forward a stronger nominee to run against Republicans. Yet it remains an open question whether voters would be open to effectively a third term of President Barack Obama, since Biden is tightly linked to every achievement and shortfall of the administration.

Liberals have rallied behind Sen. Bernie Sanders, the Democratic socialist from Vermont, but his general election prospects are far from certain.

Biden, 72, has a large and loyal collection of friends and advisers from more than four decades in Washington. Yet even inside his sprawling constellation, affectionately known as \"Biden World,\" deep divisions exist over the wisdom of him making another bid for the presidency.

Conversations this week with people close to Biden, from his home base in Delaware to Washington and beyond, suggest agreement on three points: He has not made up his mind. Anyone who believes he has is wrong. And he should be allowed to decide on his own timeframe.

\"It is very late in the presidential cycle to build the infrastructure, but the vice president enjoys a unique level of experience and respect,\" said Sen. Chris Coons, a Delaware Democrat, who is staying neutral until Biden decides. \"He has the ability to wait later in this process than almost any other Democrat.\"

Two months after his oldest son, Beau, died of brain cancer, the vice president has slowly returned to his duties at the White House and his residence at the Naval Observatory, where he invited lawmakers over Thursday to discuss the Iran nuclear deal. Friends say he is still grieving, which is also why he feels no urgency to make a decision and has not intensely focused on the presidential race.

But Biden's future is suddenly being examined in a new context, several Democrats partial to Biden say, in the wake of lingering questions about whether Clinton or her aides mishandled classified information on the private email server she used as secretary of state.

Closing window?

Even as his admirers implore him to consider running, many other Democrats believe the realistic window is closing, particularly fundraisers and key activists who play a critical role in selecting the party's nominee. Clinton has moved swiftly to lock up support from many of those so-called superdelegates, which would complicate efforts to slow her momentum as the party's frontrunner.

Roxanna Moritz, the Democratic auditor of Scott County in Iowa, had been holding out hope that she would hear from Biden. She was inspired by a grassroots Draft Biden movement and believed he would be the strongest nominee for the Democratic Party. But the only calls she received were from the campaigns of Clinton and Bernie Sanders, so she made a decision two weeks ago.

\"I signed on with Hillary,\" Moritz said Friday. \"It was hard to make that choice for me because I'm very attached to Biden. Personally, I like the man. I like the values he's brought to the country. But it seems like he's being steamrolled. I think it would be hard for him to catch up.\"

Yet the silence from Biden hasn't sapped the hope from all of his supporters, even though they recognize his focus is elsewhere.

\"I don't think he's ready yet,\" said Mary Carey Foley, a top Biden supporter in New Hampshire, who last spoke to the vice president at Beau Biden's funeral in early June.

\"He's devastated. His head is in it, but his heart has to catch up,\" she said. \"And Joe Biden has a big heart.\"

Supporters like Foley say Biden appeared inclined to mount a bid before his son fell ill, and had begun mapping out a fundraising plan to compete with the massive hauls many expect Clinton to pull in.

His family -- including Beau, before his death -- have encouraged a run, though any talk of politics was put on hold during the mourning period. On Saturday, New York Times columnist Maureen Dowd reported that as Beau Biden was dying, he tried to make his father promise to run in 2016 in an effort to not let the presidency be turned back over to the Clintons.

\"Dad, it's who you are,\" Hunter said, joining his brother, Dowd reported.

The vice president's office has declined interview requests and has issued the same statement for weeks about Biden's intentions.

'Difficult time'

\"The Biden family is going through a difficult time right now,\" Kendra Barkoff, a Biden spokeswoman, said Friday. \"Any speculation about the views of the vice president or his family about his political future is premature and inappropriate.\"

Still, the latest CNN national poll finds 15% of Democratic and Democratic-leaning registered voters are behind Biden, just a bit behind Sanders' 19%. He also tops the second-choice list with 37% of Democratic registered voters choosing him. Among those who say Clinton is their first choice, he's the clear leader as a second choice, with 50% of Clinton backers saying Biden's their next pick.

The group Draft Biden, established to encourage a run by the vice president, say supporters have held more than 400 events in 21 different states in recent months. Momentum for a Biden run hasn't slowed, organizers say, as Clinton begins laying out policy positions in early voting states.

\"Democratic supporters are hungry for a race. They want a lively debate,\" said Will Pierce, Draft Biden's executive director. He said he feared \"Democratic falloff\" if Clinton doesn't face a challenger that voters believe could be elected president.

The group has also ramped up its fundraising efforts.

Jon Cooper, a former Obama fundraiser who serves as Draft Biden's National Finance Chair, said his conversations with Democratic donors has left him convinced the vice president could raise the cash needed to compete against Clinton. The bond between Biden and Obama has grown closer in the second term and Biden is seen again and again at the president's side.

\"Partly because of the very deep reservoir of support we'll find among Obama supporters, bundlers and donors, I think the Biden campaign will be able to tap into that overnight,\" he said. \"He will be able literally within 24 hours put a strong fundraising structure in place.\"