Progressive US Senator Bernie Sanders ended his second Presidential bid on Wednesday, leaving Democratic front-runner Joe Biden to face President Donald Trump in the November 2020 election.
Mr Sanders announced his decision in a livestream from his home state of Vermont, after successive losses to Mr Biden.
He fell behind in the delegates count by more than 300 – 1,217 to 914 – which made it implausible for him to catch up with Mr Biden.
A candidate needs 1,991 delegates to take the nomination.
Mr Sanders, the first openly socialist candidate to come this far in the nomination, spoke of an ideological victory for his movement.
He said the country had moved in his direction on issues related to "medicare for all", raising the minimum wage and economic justice.
But Mr Sanders acknowledged that the maths was no longer in his favour.
“I wish I can give you better news but our path for victory is virtually impossible,” he said.
Mr Sanders, 78, said quitting the campaign was a painful decision.
He said the coronavirus pandemic was the main reason behind his exit.
“As I see a crisis ripping the nation, I cannot in good conscience continue to mount a campaign that cannot win,” Mr Sanders said.
He congratulated Mr Biden on becoming the presumptive nominee but stopped short of endorsement.
Mr Sanders said Mr Biden was “a very decent man”.
He then quipped that he could stay on to accumulate delegates in the remaining states, not to win the nomination, but to exert influence and shape the party platform at the convention that will officially declare the winner in August.
Mr Biden praised the Sanders campaign and the senator, with whom he had long been friends.
“I want to commend Bernie for being a powerful voice for a fairer and more just America," the former vice president said.
"Together we will defeat Donald Trump. And when we do that, we’ll not only do the hard work of rebuilding this nation, we’ll transform it."
Mr Biden also addressed Mr Sanders's supporters, some of whom broke with the party in 2016 and voted for Mr Trump or a third candidate over former nominee Hillary Clinton.
“And to Bernie’s supporters: I know that I need to earn your votes. And I know that might take time," he said.
"But I want you to know that I see you, I hear you and I understand the urgency of this moment.
"I hope you'll join us. You're more than welcome: You're needed."
But Mr Trump, who has long exploited divisions in the Democratic Party, called on Sanders supporters to join the Republicans
"The Bernie people should come to the Republican Party, trade," he tweeted.
The latest polls have shown Mr Trump trailing Mr Biden and Mr Sanders.
The coronavirus and a looming recession in the US have hurt the president’s standing.
It is now likely that Mr Biden will seek high-level endorsements from former president Barack Obama, former candidate Senator Elizabeth Warren, former first lady Michelle Obama, and Bill and Hillary Clinton.
Mr Biden called Mr Sanders last week to tell him he was forming a search committee to help pick a candidate for vice president.
He announced last month that he would pick a woman for the job.
Leading names include senators Kamala Harris, Amy Klobuchar, Ms Warren and Catherine Cortez, and governors Gretchen Whitmer and Michelle Lujan Grisham.
