Bernie Sanders launched a series of attacks on Joe Biden as he sought to halt the former vice president’s political momentum ahead of several crucial primaries that may decided who takes on Donald Trump in November. For his part, Mr Biden stood his ground and delivered one of his most impressive performances to date.

In a Democratic Party debate overshadowed and partly taken up by the global coronavirus crisis – the two septuagenarians debated in an empty television studio and touched elbows rather than shaking hands – the two men both make their case why they were better placed to defeat Mr Trump.

Yet, they were united in their condemnation of the president, not least for what they said was the faltering way his administration had responded to the crisis that had killed at least 60 Americans and infected at least 3,300.

“This is bigger than any one of us – this calls for a national rallying for one another,” said Mr Biden.

Mr Sanders used the the crisis to defend one of his signature policy proposals – universal healthcare.

Democratic primaries: Who won where? Show all 27 1 /27 Democratic primaries: Who won where? Democratic primaries: Who won where? Arizona: Biden wins Joe Biden: 39 delegates Bernie Sanders: 28 delegates Getty Democratic primaries: Who won where? Alabama: Biden wins Joe Biden: 41 delegates Bernie Sanders: 7 delegates Michael Bloomberg: 1 delegate Reuters Democratic primaries: Who won where? Arkansas: Biden wins Joe Biden: 17 delegates Bernie Sanders: 9 delegates Michael Bloomberg: 5 delegates AFP/Getty Democratic primaries: Who won where? California: Sanders wins Bernie Sanders: 179 delegates Joe Biden: 127 delegates Michael Bloomberg: 15 delegates Elizabeth Warren: 5 delegates AP Democratic primaries: Who won where? Colorado: Sanders wins Bernie Sanders: 20 delegates Joe Biden: 9 delegates Michael Bloomberg: 9 delegates Elizabeth Warren: 1 delegate AFP/Getty Democratic primaries: Who won where? Florida: Biden wins Joe Biden: 152 delegates Bernie Sanders: 53 delegates Getty Democratic primaries: Who won where? Idaho: Biden wins Joe Biden: 11 delegates Bernie Sanders: 9 delegates EPA Democratic primaries: Who won where? Illinois: Biden wins Joe Biden: 95 delegates Bernie Sanders: 59 delegates AFP Democratic primaries: Who won where? Iowa: Buttigieg wins Pete Buttigieg: 14 delegates Bernie Sanders: 12 delegates Elizabeth Warren: 8 delegates Joe Biden: 6 delegates Amy Klobuchar: 1 delegates Reuters Democratic primaries: Who won where? Maine: Biden wins Joe Biden: 11 delegates Bernie Sanders: 9 delegates Elizabeth Warren: 4 delegates AFP/Getty Democratic primaries: Who won where? Massachussetts: Biden wins Joe Biden: 37 delegates Bernie Sanders: 29 delegates Elizabeth Warren: 25 delegates AP Democratic primaries: Who won where? Michigan: Biden wins Joe Biden: 72 delegates Bernie Sanders: 52 delegates Getty Democratic primaries: Who won where? Minnesota: Biden wins Joe Biden: 38 delegates Bernie Sanders: 27 delegates Elizabeth Warren: 10 delegates Reuters Democratic primaries: Who won where? Mississippi: Biden wins Joe Biden: 34 delegates Bernie Sanders: 2 delegates AFP via Getty Images Democratic primaries: Who won where? Missouri: Biden wins Joe Biden: 44 delegates Bernie Sanders: 24 delegates AP Democratic primaries: Who won where? Nevada: Sanders wins Bernie Sanders: 24 delegates Joe Biden: 9 delegates Reuters Democratic primaries: Who won where? New Hampshire: Sanders/Buttigieg tie Bernie Sanders: 9 delegates Pete Buttigieg: 9 delegates Amy Klobuchar: 6 delegates EPA Democratic primaries: Who won where? North Carolina: Biden wins Joe Biden: 66 delegates Bernie Sanders: 36 delegates Elizabeth Warren: 2 delegates Michael Bloomberg: 2 delegates AFP/Getty Democratic primaries: Who won where? North Dakota: Sanders wins Bernie Sanders: 8 delegates Joe Biden: 6 delegates Getty Democratic primaries: Who won where? Oklahoma: Biden wins Joe Biden: 21 delegates Bernie Sanders: 13 delegates Michael Bloomberg: 2 delegates Elizabeth Warren: 1 delegate Reuters Democratic primaries: Who won where? Florida: Biden wins Joe Biden: 152 delegates Bernie Sanders: 53 delegates Getty Democratic primaries: Who won where? Tennessee: Biden wins Joe Biden: 33 delegates Bernie Sanders: 18 delegates Michael Bloomberg: 10 delegates Elizabeth Warren: 1 delegate Reuters Democratic primaries: Who won where? Texas: Biden wins Joe Biden: 111 delegates Bernie Sanders: 102 delegates Michael Bloomberg: 10 delegates Elizabeth Warren: 5 delegates Reuters Democratic primaries: Who won where? Utah: Sanders wins Bernie Sanders: 12 delegates Joe Biden: 2 delegate Michael Bloomberg: 2 delegates AFP/Getty Democratic primaries: Who won where? Vermont: Sanders wins Bernie Sanders: 11 delegates Joe Biden: 5 delegates AP Democratic primaries: Who won where? Virginia: Biden wins Joe Biden: 66 delegates Bernie Sanders: 31 delegates Elizabeth Warren: 2 delegates AFP/Getty Democratic primaries: Who won where? Washington: Biden wins Joe Biden: 46 delegates Bernie Sanders: 43 delegates AP

“One of the reasons that we are unprepared, and have been unprepared, is we don’t have a system. We’ve got thousands of private insurance plans,” he said.

“That is not a system that is prepared to provide health care to all people in a good year, without the epidemic.”

The debate – technically the 11th the party has held to help choose a presidential nominee – was unusual in several ways, other than the impact of coronavirus, which had led the organisers to switch the location from Arizona to Washington DC.

It was the first to involve a showdown between the two men who have come to represent different ideological strands within the party battling out. Indeed, while congresswoman Tulsi Gabbard is still win the race, she did not qualify for the debate.

It may also be noteworthy for being the last debate.

Biden attacks Sanders over 'you're full of s**t' pile-on

Despite winning in Iowa, New Hampshire and Nevada, Mr Sanders, 78, has seen his frontrunner status taken away by the 77-year-old Mr Biden, following big wins in South Carolina and on Super Tuesday.

Mr Biden followed up with more successes last Tuesday, and looks poised to add to his delegate count this coming week, when Florida, Illinois, Ohio and Arizona hold their primaries.

An average of polls collated by RealClearPolitics gives Mr Biden a lead of up to 20 points in each state. Nationally, he is also beating Mr Sanders by 20 points.

Mr Biden currently has 890 delegates, compared to 736 for Mr Sanders. In addition, the Vermont senator would require to win around 57 per cent of those remaining.

Commentators say Mr Sanders is most likely staying in the race to try and secure some policy concessions from Mr Biden, who will need the backing of the senator’s young and enthusiastic voters.

On Sunday, both men vowed to support and campaign for the other should they win. Yet they also laid into each other over everything from Mr Biden’s vote to support the invasion of Iraq, to Mr Sanders’ words of praise for Cuba’s education system.

“These are flat-out dictators, period, and they should be called for it, straight-up,” said Mr Biden.

Mr Sanders replied: “We condemn authoritarianism whether it’s in China, Russia, Cuba, anyplace else. But to simply say that nothing ever done by any of those administrations had a positive impact on their people would, I think, be incorrect.”