US Vice-President Joe Biden will not run for president next year, ending months of speculation and clearing the way for Democratic front runner Hillary Clinton.
"Unfortunately, I believe we are out of time, the time necessary to mount a winning campaign for the nomination," he said at the White House Rose Garden on Wednesday.
"But while I will not be a candidate, I will not be silent," he said, adding he intends to speak out to influence his party and the direction Americans should take as a nation.
Mr Biden, 72, had spent the last few months considering a bid for the White House while mourning his son Beau, who died of brain cancer in May.
The younger Biden, who was the Delaware state attorney-general, had encouraged his father to run.
It would have been Mr Biden's third attempt, having failed to gain traction in 1988 and 2008, and many believe he has made the right call.
"He has run and lost two times before, and he waited so long - there comes a point when it is too late to raise money and get organised," said Dr Melissa Miller, associate professor of political science at Bowling Green State University (BGSU) in Ohio.
His decision is a major boost for the Clinton campaign, as Mr Biden's supporters are now likely to turn to Mrs Clinton as their candidate.
Said Assistant Professor Kelly Winfrey of the Carrie Chapman Catt Centre for Women and Politics at Iowa State University: "I would imagine she (Clinton) is relieved not to have another competitor. With recent polls showing Bernie Sanders losing ground, Hillary gaining after the debate, and Biden choosing not to enter the race, I think it has been a good week for Clinton."
A poll released on Wednesday by BGSU showed that in the key state of Ohio, Mrs Clinton would get 38.2 per cent of the vote among Democratic primary voters with Mr Biden in the race, but her vote share would jump to 53.8 per cent with him out of the running.
University of North Florida assistant professor of political science Michael Binder said a university survey released on Wednesday showed that 71 per cent of Biden supporters had picked Mrs Clinton as their second choice, while only 17 per cent chose Mr Sanders.
"Both (Clinton and Biden) are establishment Democrats and he would have pulled from her base... Hillary is the big winner today," said Professor Binder.
In a statement, Mrs Clinton called Mr Biden "a good man and a great vice-president" and said she was confident that he would continue to be "on the front lines, always fighting for all of us".
Mr Biden, however, took a swipe at his former colleague during his speech. "I don't think that we should look at Republicans as our enemies. They are opposition. They are not our enemies. And for the sake of the country, we have to work together," he said.
Mrs Clinton had referred to Republicans as her enemies during the first Democratic debate last week.
Mr Biden also seemed to chide her for her opposition to the Trans- Pacific Partnership trade deal, which she had previously supported while in the Obama administration.
"This party, our nation, will be making a tragic mistake if we walk away or attempt to undo the Obama legacy... Democrats should not only defend and protect this record, but they should run on the record," he said.
Republicans generally used the news as another opportunity to attack Mrs Clinton's campaign.
Republican National Committee chairman Reince Priebus said that "Vice-President Biden was the most formidable candidate the Democratic Party could have fielded" and his decision not to run would improve his party's chances of taking back the White House.
In the same vein, Republican candidate Donald Trump tweeted: "Personally I would rather run against Hillary because her record is so bad."