Joe Biden’s reinvigorated primary campaign received another boost with the withdrawal from the race of billionaire Mike Bloomberg who then endorsed the former vice-president for the White House.

Mr Biden’s campaign has caught fire in the last few days after Bernie Sanders had made the early running in the process that will determine which Democrat challenges President Donald Trump for the keys to the Oval Office in November.

Mr Bloomberg entered the race on Super Tuesday but his poor showing was a stunning collapse for the former New York City mayor, who had his 2020 hopes and pumped more than 500 million US dollars of his own fortune into the campaign.

Mr Bloomberg announced his departure from the race after a disappointing finish on Super Tuesday in the slate of states that account for almost one-third of the total delegates available in the Democratic nominating contest.

He won only the territory of American Samoa and picked up several dozen delegates elsewhere.

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(PA Graphics)

Elizabeth Warren was also reported to be reconsidering her candidacy in a race which looks more and more like a duel between Mr Biden and Mr Sanders.

Mr Biden, meanwhile, won big in Southern states where Mr Bloomberg had poured tens of millions of dollars and even cautiously hoped for a victory.

Election 2020 Joe Biden
Democratic presidential candidate former vice president Joe Biden (Chris Carlson/PA)

“Three months ago, I entered the race for President to defeat Donald Trump,” Mr Bloomberg said in a statement.

“Today, I am leaving the race for the same reason: to defeat Donald Trump — because it is clear to me that staying in would make achieving that goal more difficult.”

Two of Mr Bloomberg’s former Democratic rivals, Amy Klobuchar and Pete Buttigieg, dropped out of the race and endorsed Mr Biden as the moderate alternative to Mr Sanders just the day before Super Tuesday.

Mr Biden, who served as vice-president to Barack Obama, has seen his campaign reignited over the past few days after disappointing opening performances in Iowa and New Hampshire, which are overwhelmingly white states.

Following his victory in South Carolina, he built on that success on Super Tuesday and now can count on the support of several of his former rivals.

Mr Trump, meanwhile, had taunted Democrats for, in his view, ganging up on Mr Sanders and had urged Ms Warren to quit the race.

Reacting to Mr Bloomberg’s withdrawal, Mr Trump tweeted: “Mini Mike Bloomberg just “quit” the race for President. I could have told him long ago that he didn’t have what it takes, and he would have saved himself a billion dollars, the real cost. Now he will pour money into Sleepy Joe’s campaign, hoping to save face. It won’t work!”

He added: “Mini Mike Bloomberg will now fire Tim O’Brien, and all of the fools and truly dumb people who got him into this mess. This has been the worst, and most embarrassing, experience of his life…and now on to Sleepy Joe!”

He urged Ms Warren to quit the race and suggested it had harmed Mr Sanders’ White House bid.

The president tweeted: “Wow! If Elizabeth Warren wasn’t in the race, Bernie Sanders would have easily won Massachusetts, Minnesota and Texas, not to mention various other states. Our modern day Pocahontas won’t go down in history as a winner, but she may very well go down as the all time great spoiler!”