As the two remaining Democratic candidates curb their public events in the face of the coronavirus outbreak, Joe Biden has opened up a massive lead over Bernie Sanders in the crucial state of Florida.

With just days to go before the state votes alongside three other states on 17 March, the University of North Florida survey finds Mr Biden outpacing Mr Sanders by 44 points. If that finding is borne out when the state votes, it would be one of Mr Sanders’s most severe defeats of the whole primary season.

Mr Sanders has already been all but written off by observers after a string of heavy losses in large states. His standing in Florida has been badly hurt by his past comments on Fidel Castro and other Latin American socialists, and he is also polling well behind Mr Biden in the other states voting on 17 March – Arizona, Illinois and Ohio, all of which he lost to Hillary Clinton in 2016.

And to make matters worse, while he will still debate Mr Biden at a scheduled TV encounter on 15 March, the room will be devoid of one of his most valuable assets: an audience.

Mr Sanders trades heavily on his ability to draw a massive crowd, whom he whips into a frenzy with his calls for a political revolution to overthrow “the establishment”. But with numerous states now banning large public gatherings to try and stop the spread of coronavirus, such events have quickly become taboo.

Both Mr Sanders and Mr Biden decided against holding large rallies after the primaries on 10 March.

Steve Schmidt, McCain's top adviser, told Fortune the outbreak was particular tough on Sanders' campaign.

"The raw politics of this is that it freezes the Democratic race in place for Bernie Sanders, who is on his last legs. You can't have a revolution without rallies," he said.

Mr Biden, who triumphed in four of the six states voting that day, addressed a small crowd in Philadelphia, while Mr Sanders declined to hold an event at all, instead giving a televised speech in Burlington, Vermont the next day.

In the address, he maintained he was still in the race and confirmed he would debate Mr Biden before the next primaries, but conceded he was falling well behind in terms of delegates. Much of the speech was framed as a set of challenges to Mr Biden to embrace progressive causes – and the absence of a cheering audience was all too conspicuous.