For more than three years it seemed impossible to millions of Americans that anything could be more important than voting for an alternative to Donald Trump.

Yet right now the US president is no longer seen as the most pressing threat to national security. The coronavirus crisis has temporarily turned the US presidential election into a sideshow.

It was Senator Bernie Sanders who compared it in scale to “a major war” and suggested it may result in more casualties than the US military suffered against Germany and Japan in the second world war.

Now Sanders, who suffered another drubbing in Tuesday’s Democratic primaries in Arizona, Florida and Illinois, is facing calls to make a gesture worthy of wartime and call it quits for the national good. “#DropOutBernie” is trending on Twitter.

By throwing his weight behind Biden, the argument goes, he would in effect be doing a Clement Attlee – the Labour leader who agreed to serve under his rival, Conservative Winston Churchill, in Britain’s coalition government when Sanders was born in 1941.

Such a gesture would ease fears over the primary elections themselves being a public health risk – rallies are off and Ohio postponed its vote at the last minute – and enable Biden to focus on the twin priorities of the coronavirus and Trump.

Sanders “would do public health and the party he has twice aspired to lead a big favor by acknowledging reality and leaving the race now”, David Byler, a data analyst and political columnist, wrote in the Washington Post.

“By officially making former vice-president Joe Biden the presumptive nominee, Sanders would free Democrats to make more rational decisions about how and when to hold their contests, and could free voters from making an impossible choice between casting their ballots and safeguarding their health.”

Supporters of this view point to simple maths. After the results of Tuesday night, Biden is more than 300 delegates ahead of Sanders, a virtually unassailable lead. Having never won a state in his first two runs for president, 77-year-old Biden is now racking them up. The virus only strengthens his case as the restorer of order and experience in a White House currently run chaotically by a TV star.

On Tuesday, as expected, Biden gained nearly two-thirds of the vote in the vital swing state of Florida, where Sanders’ recent comments in praise of the Cuban revolutionary Fidel Castro’s literacy programme played badly. He also hammered the senator in Illinois by a bigger margin than Hillary Clinton managed in 2016, winning every county but one, and claimed Arizona to boot.

It has been a stunning turnaround since the dark days of Iowa and New Hampshire and is now all over bar the shouting.

The former vice-president evidently believes so. In remarks on Tuesday night that again lacked an audience for safety reasons, he said: “Senator Sanders and I may disagree on tactics, but we share a common vision – from the need to provide affordable healthcare for all Americans to reducing income inequality to taking on climate change.”

He added: “And let me say, especially to the young voters who have been inspired by Senator Sanders: I hear you. I know what is at stake. And I know what we have to do.”

Biden has already begun courting progressive voters by backing a version of Sanders’ plan to make public colleges and universities tuition-free for many students and Senator Elizabeth Warren’s proposal to overhaul the consumer bankruptcy system.

Yet there are still reasons to believe that Sanders will refuse to wave the white flag. He kept going last Sunday for a head-to-head debate without an audience in a TV studio in Washington. On Tuesday, even as the grim results trickled in, he released his “coronavirus crisis principles” that “include at least $2 trillion in funding to mobilize on a scale not seen since the New Deal and World War II to prevent deaths, job losses, and economic ruin”.

And no one in the Democratic party has forgotten Sanders’ tenacity/obstinacy – take your pick – in 2016 when he refused to surrender against Clinton. Back then, there was always the possibility that an FBI investigation into her poor email hygiene could scuttle her candidacy. There is no such shadow hanging over Biden.

A Sanders concession would not be simple, however. Some of his supporters never made peace with Clinton and would naturally reject Democratic National Committee pressure to wind up the election prematurely. Some are deeply sceptical of Biden as yet another centrist incrementalist who represents the past rather than the future. They will argue that not even the coronavirus should postpone the revolution.

Two dozen other candidates have come and gone, realising when it was the right moment to leave the stage. Now all eyes are on Sanders, with many entreating him to take his final bow from presidential politics.

The 78-year-old launched his first long-shot campaign at a hastily arranged press conference on a patch of grass known as the Senate swamp on Capitol Hill five years ago next month. He attracted only a small group of reporters; none could have guessed what a movement he would build.

It will be a movement in search of a new leader. And it is a movement whose support the Democratic party needs to beat Trump. The current president offers plenty of negative reasons to vote in November. Now Biden must offer enough positive ones.