Former White House candidate Bernie Sanders on Monday endorsed onetime rival Joe Biden for president, saying it was time to unite in the effort to defeat Donald Trump in November.  

The two veteran politicians, who each spent the past year battling for the Democratic nomination, appeared together by split-screen on Biden's livecast.

"Today I am asking all Americans – I'm asking every Democrat, I'm asking every independent, I'm asking a lot of Republicans – to come together in this campaign to support your candidacy which I endorse," Sanders said.  

The swift backing marked a notable change from 2016, when Sanders lost the presidential nomination race to Hillary Clinton but delayed endorsing her candidacy. That wait was seen as deeply damaging in that it exposed a divide within the Democratic Party.  

Sanders struck a unifying tone on Monday, telling viewers "it's imperative that all of us work together."  

The 78-year-old independent leftist senator from Vermont exited the 2020 race last week after losing almost all of the primary contests following a strong start, leaving Biden as the party's presumptive nominee. 

The deadly coronavirus pandemic has forced a suspension of all in-person political campaigning, as most of the nation remains under stay-at-home orders – including Biden and Sanders, who appeared online from their homes.  
Sanders on Monday signaled it was crucial to unite around Biden's campaign to defeat Trump, whom Sanders branded "the most dangerous president in the modern history of this country."  

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Biden said he was "deeply grateful" for the endorsement. "You've been the most powerful voice for a fair and more just America," he told Sanders.  

"You've put the interests of this nation and the need to beat Donald Trump above all else," Biden added. "As you say, 'not me, us.'"  

Biden, who at 77 is mounting his third presidential run, also appealed to Sanders supporters. "I see you, I hear you, I understand the urgency of what it is that we have to get done in this country, and I hope you'll join us," Biden said. "I'm going to need you badly."

Biden announced the two men were establishing several policy working groups to address issues like climate change, healthcare, economic justice and college affordability. Sanders has been more liberal on such issues than Biden, and has successfully brought them front and center in the campaign, especially his call for a government-managed universal healthcare system.  

Trump's re-election campaign said in a statement that Biden has "had to adopt most of Bernie's agenda" – policies that Trump has branded socialist.  

"President Trump's supporters will run through a brick wall to vote for him. Nobody is running through a brick wall for Joe Biden," Trump 2020 campaign manager Brad Parscale said in a statement.  

Trump's approval rating has ticked up in the last few weeks of the pandemic, even as the U.S. death toll soared past 20,000, a global high. But in a series of polls conducted this month, Biden leads Trump in head-to-head general election matchups by an average of 5.9 percent, according to the RealClearPolitics website. 

Meanwhile, Biden was projected the Associated Press on Monday to be the winner of Wisconsin's Democratic presidential primary, as results began to be released in state elections last week. 

(With input from AFP, Reuters)