WASHINGTON: United States Vice President Joe Biden said on Wednesday he would not run for president in 2016, ending months of indecision and removing one of Democratic front-runner Hillary Clinton's biggest potential obstacles to the party's nomination.

Biden, who had been pondering a run since August, appeared in the White House Rose Garden with wife Jill and President Barack Obama to say the window for mounting a successful campaign had closed.

“While I will not be a candidate, I will not be silent,” Biden said. “I intend to speak out clearly and forcefully to influence as much as I can where we stand as a party and where we need to go as a nation.”

Biden, 72, had been wrestling with doubts about whether he and his family were ready for a grueling campaign while still mourning his son Beau, who died of brain cancer in May. His son had urged him to run.

His decision was a boost for Clinton, whose prime challenger now is US Senator Bernie Sanders of Vermont. A self-styled democratic socialist, Sanders has galvanized the party's left wing but has yet to prove he can broaden his appeal.

“It's an easier path for Hillary Clinton now,” said Democratic strategist Bud Jackson. “Most polls reflect that without Biden in the race, it's more beneficial to her.”

His decision also ends a highly public, months-long “will he or won't he?” political guessing game about Biden's intentions which had shadowed Clinton's campaign and frozen the support of Democratic activists and donors.

“It solidifies and crystallises the race. There will be no late entries. There will be no more what ifs,” said Democratic strategist Rodell Mollineau.

Out of time

Jumping into the race so late would have been a huge challenge to Biden, who would have had to quickly build a fundraising network and campaign structure ahead of the first nominating contest in Iowa on February 1.

“Unfortunately, I believe we're out of time, the time necessary to mount a winning campaign for the nomination,” Biden said in the Rose Garden.

“The process doesn't respect or much care about filing deadlines or debate or primaries and caucuses. But I also know I couldn't do this if the family isn't ready.”

Biden, who is popular with white, working-class voters, could still play a major role and become a valuable surrogate for Democrats against the Republican nominee in the general election campaign. He urged Democrats to defend and run on Obama's record.

Republican presidential front-runner Donald Trump said on Twitter that he preferred to run against Clinton anyway because “her record is so bad.”

Also in the running for the Democratic nomination are former Maryland Governor Martin O'Malley and former Rhode Island Governor Lincoln Chafee.

This party, our nation, will be making a tragic mistake if we walk away or attempt to undo the Obama legacy,” Biden said.

In a statement, Clinton called Biden “a good man and a great vice president” and said she was confident he would continue to be on the political front lines “fighting for all of us.” The door to a late bid by the affable Biden had cracked open over perceptions, fueled by controversy over her use of a private email server while secretary of state, that Clinton was both failing to connect with voters and untrustworthy.

But what was widely hailed as a command performance by Clinton in the Oct. 13 Democratic debate turned the tide back in her favor and quieted talk that she was vulnerable in her quest for her party's nomination for the November 2016 election.

Support up for Clinton

Clinton's support among Democrats surged by 10 percentage points after the October debate, a Reuters/Ipsos poll showed. She had the backing of about 52 percent of poll participants, followed by Sanders at 27 percent. Biden's support, at 13 percent, was down 6 percentage points.

A White House official, speaking on condition of anonymity, said Biden made his decision not to run last night.

A separate official, White House spokesman Eric Schultz, said Obama had served as a “sounding board” for Biden during the process.

“That's not just as he copes with unspeakable loss, but also as he makes very personal decisions about his political future,” Schultz, traveling with Obama, told reporters on Air Force One after Biden spoke.

Biden had run for president in 1988 and 2008, both times failing to gain traction despite more than three decades as a US Senator from Delaware.

He has been prominent for a vice president, with broad involvement in many of Obama's foreign affairs decisions, such as the withdrawal from Iraq and his Afghanistan strategy.

He also became something of a secret weapon for the White House on Capitol Hill, stepping in to negotiate tricky fiscal deals with Republican lawmakers.