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.

Photos: Who's running for president? Photos: Who's running for president? Ted Cruz, Donald Trump, John Kasich, Hillary Clinton and Bernie Sanders, Hide Caption 1 of 6 Photos: Who's running for president?



"So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Businessman Donald Trump announced June 16 at his Trump Tower in New York City that he is seeking the Republican presidential nomination. This ends more than two decades of flirting with the idea of running for the White House."So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Hide Caption 2 of 6 Photos: Who's running for president?



"These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Sen. Ted Cruz of Texas has made a name for himself in the Senate, solidifying his brand as a conservative firebrand willing to take on the GOP's establishment. He announced he was seeking the Republican presidential nomination in a speech on March 23."These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Hide Caption 3 of 6 Photos: Who's running for president? Ohio Gov. John Kasich joined the Republican field July 21 as he formally announced his White House bid.



"I am here to ask you for your prayers, for your support ... because I have decided to run for president of the United States," Kasich told his kickoff rally at the Ohio State University. Hide Caption 4 of 6 Photos: Who's running for president?



"Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hillary Clinton launched her presidential bid on April 12 through a video message on social media. The former first lady, senator and secretary of state is considered the front-runner among possible Democratic candidates."Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hide Caption 5 of 6 Photos: Who's running for president?



"This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Sen. Bernie Sanders , an independent from Vermont who caucuses with Democrats, announced his run in an email to supporters on April 30. He has said the United States needs a "political revolution" of working-class Americans to take back control of the government from billionaires."This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Hide Caption 6 of 6

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.

Photos: Photos: Vice President Joe Biden Photos: Photos: Vice President Joe Biden U.S. Vice President Joe Biden began his career in politics in 1972, winning election to the Senate at the age of 29 (he was 30 when he took office). The Delaware Democrat was reelected to the Senate six times, including 2008, before becoming the 47th vice president of the United States. Hide Caption 1 of 14 Photos: Photos: Vice President Joe Biden Biden is sworn in for his second term as vice president by Supreme Court Justice Sonia Sotomayor, with his wife, Jill, and son, Beau, by his side, on January 21, 2013, in Washington. Hide Caption 2 of 14 Photos: Photos: Vice President Joe Biden Biden presides over a ceremony in Baghdad to formally mark the end of the U.S. combat mission in Iraq on September 1, 2010. Hide Caption 3 of 14 Photos: Photos: Vice President Joe Biden Biden and President-elect Barack Obama wave to the crowd at their election night party at Grant Park in Chicago on November 4, 2008. Hide Caption 4 of 14 Photos: Photos: Vice President Joe Biden Biden speaks after being introduced as Obama's running mate while campaigning together after the Democratic National Convention in 2008. Hide Caption 5 of 14 Photos: Photos: Vice President Joe Biden From left, former Sen. John Edwards, Biden, Obama and Sen. Hillary Clinton at a debate of Democratic presidential candidates on April 26, 2007, in Orangeburg, South Carolina. Hide Caption 6 of 14 Photos: Photos: Vice President Joe Biden Biden releases his memoir, "Promises to Keep: On Life and Politics," in 2007. Hide Caption 7 of 14 Photos: Photos: Vice President Joe Biden As a ranking member of the Senate Foreign Relations Committee, Biden is interviewed on NBC's "Meet the Press," concerning the war in Iraq on August 14, 2005. Hide Caption 8 of 14 Photos: Photos: Vice President Joe Biden While chairman of the Senate Foreign Relations Committee, Biden meets Afghan students during a visit to Kabul in 2002. Hide Caption 9 of 14 Photos: Photos: Vice President Joe Biden Biden is welcomed back after undergoing surgery for an aneurysm in 1988. Hide Caption 10 of 14 Photos: Photos: Vice President Joe Biden Biden announces his candidacy for the Democratic presidential nomination in 1988. After three months he drops out, following reports of plagiarism and false claims about his academic record. Hide Caption 11 of 14 Photos: Photos: Vice President Joe Biden While on the Senate Judiciary Committee, Biden meets with Sen. Frank Church, center, and Egyptian President Anwar Sadat after the signing of the Egyptian-Israeli Peace Treaty in 1979. Hide Caption 12 of 14 Photos: Photos: Vice President Joe Biden President Jimmy Carter and Biden attend a reception for the Delaware Democratic Party in 1978. Biden was the first senator to endorse Carter's presidential candidacy two years earlier. Hide Caption 13 of 14 Photos: Photos: Vice President Joe Biden At a convention in 1972, Biden and his first wife, Neilia, and his two sons take a photo with Delaware Gov.-elect Sherman W. Tribbitt and his wife Jeanne. Neilia Biden died in a car accident a few months later, after his first election to the Senate, along with their infant daughter, Naomi. Hide Caption 14 of 14

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."

Photos: Beau Biden mourned Photos: Beau Biden mourned Mourners exit St. Anthony of Padua Catholic Church after a Mass of Christian burial was held for former Delaware Attorney General Beau Biden on Saturday, June 6, in Wilmington. Biden, Vice President Joe Biden's eldest son, died at the age of 46 after a battle with brain cancer. Hide Caption 1 of 17 Photos: Beau Biden mourned Vice President Joe Biden and his wife, Jill Biden, depart after the service on June 6. Hide Caption 2 of 17 Photos: Beau Biden mourned Chris Martin of Coldplay performs "Til Kingdom Come" during the funeral. Hide Caption 3 of 17 Photos: Beau Biden mourned President Barack Obama hugs Joe Biden after delivering the eulogy on June 6. In his eulogy, Obama credited the vice president with inspiring in his son a devotion to public service and to family, jokingly calling him "Joe 2.0." Hide Caption 4 of 17 Photos: Beau Biden mourned President Barack Obama delivers the eulogy in honor of Beau Biden on June 6. The President struggled for composure at several points during his tribute.

Hide Caption 5 of 17 Photos: Beau Biden mourned A procession carrying the casket of Beau Biden enters the church on June 6. Hide Caption 6 of 17 Photos: Beau Biden mourned Vice President Joe Biden, accompanied by his family, holds his hand over his heart as he watches an honor guard carry a casket containing the remains of his son into St. Anthony of Padua Roman Catholic Church in Wilmington, on June 6. Standing alongside the vice president are Beau Biden's widow Hallie Biden, left, and daughter, Natalie. Hide Caption 7 of 17 Photos: Beau Biden mourned Vice President Joe Biden and his wife Dr. Jill Biden arrive with family for the funeral on June 6. Hide Caption 8 of 17 Photos: Beau Biden mourned An honor guard stands at the viewing for Beau Biden at St. Anthony of Padua in Wilmington, Delaware on Friday June 5. Hide Caption 9 of 17 Photos: Beau Biden mourned Vice President Joe Biden and his wife, Jill, greet mourners during the viewing for Beau Biden inside St. Anthony of Padua in Wilmington, Delaware, on Friday, June 5. Hide Caption 10 of 17 Photos: Beau Biden mourned Mourners arrive for the viewing on June 5. Hide Caption 11 of 17 Photos: Beau Biden mourned Vice President Joe Biden rests his head in his hand during a viewing for his late son, former Delaware Attorney General Beau Biden, on Thursday, June 4. Standing with the vice president, from right, is his wife, Jill, and Beau Biden's immediate family: daughter Natalie, wife Hallie and son Hunter. Hide Caption 12 of 17 Photos: Beau Biden mourned An honor guard carries Biden's casket out of Legislative Hall in Dover, Delaware. Hide Caption 13 of 17 Photos: Beau Biden mourned Joe Biden pauses with his family as they enter the visitation. Hide Caption 14 of 17 Photos: Beau Biden mourned Natalie Biden, center, is comforted by her grandfather and her mother as they follow the honor guard carrying the casket. Hide Caption 15 of 17 Photos: Beau Biden mourned Biden hugs a woman while waiting in line to view his son's body. Hide Caption 16 of 17 Photos: Beau Biden mourned Biden rests his hand on the flag-draped casket. Hide Caption 17 of 17

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."