Joe Biden’s impressive victories in Florida, Illinois and Arizona this week provide him with a near-insurmountable lead in the battle for delegates to the Democratic convention which will pick the party’s presidential nominee.

Whether he throws in the towel in the coming days or not, Bernie Sanders’ hopes of making it to the White House — a dream his supporters believed was close to reality less than a month ago — is effectively over.

Mr Biden’s biggest win was in delegate-rich Florida where the Jewish vote is the largest of any state bar New York and California.

Jewish Democrats — who, polling conducted in January showed, were much cooler on Mr Sanders than Democrats as a whole — are thus likely to have contributed heavily to the Vermont senator’s defeat.

The former vice-president’s victories came after he emerged from his first — and potentially only — head-to-head debate on Sunday night with Mr Sanders unscathed.

Although it was largely dominated by discussion about the coronavirus pandemic, the Vermont senator did attack Mr Biden’s past record, but he failed to deliver the kind of knock-out blow that might change the dynamics of the race.

Mr Sanders has the cash to keep on running, but the coronavirus crisis – which has seen primary elections, including one, Ohio, which was supposed to have voted on Tuesday, delayed – will increase the pressure on him to withdraw.

The cancellation of the huge rallies which are the hallmark of his campaign deprives him of the only justification — given his delegate numbers — for continuing his campaign: the platform they provide to push his policy agenda.

Symbolically, however, it was probably his defeat in Michigan last week which did most to damage Mr Sanders’ hopes of reviving a campaign which had already been blown off course by Mr Biden’s string of victories on Super Tuesday at the start of the month.

In the hearts of Mr Sanders’ supporters, Michigan has a special place. It was his upset victory over Hillary Clinton in 2016 which gave him the momentum to continue his fight against her long into the summer.

Moreover, when Donald Trump narrowly defeated Mrs Clinton there on election night in November — thus removing a critical brick from her party’s so-called “blue wall” — it created the myth that, as the nominee, the Vermont senator might have managed to keep enough white working-class voters inside the Democratic tent to retain the White House.

Mr Biden’s emphatic win in Michigan, reinforced by the result this week from neighbouring Illinois, has revealed what many had long suspected: that Mr Sanders’ 2016 campaign was fuelled less by support for his left-wing agenda than antipathy to Mrs Clinton. 

White men, for instance, who voted heavily for Mr Sanders four years ago have swung heavily towards Mr Biden.

Moreover, for all Mr Sanders’ populist talk of being a victim of a determined “corporate media” and “Democratic establishment” to block his nomination, Mr Biden will become his party’s flag-bearer largely thanks to being the overwhelming favourite of African American voters — like Mrs Clinton four years ago. 

Moreover, for all Mr Sanders’ populist talk of being a victim of a determined “corporate media” and “Democratic establishment” to block his nomination, Mr Biden will become his party’s flag-bearer largely thanks to being the overwhelming favourite of African American voters — like Mrs Clinton four years ago. 

It is this, the party’s most loyal constituency, not the Washington elite of which Mr Sanders is himself a part, who have once again sealed his fate.

There is a paradox, though, that even as Mr Sanders ultimately succumbs once again to a centrist rival, he has helped to fundamentally reshape the Democratic party. In 2016, the price of his eventual endorsement of Mrs Clinton was a Democratic platform to the left of any in recent memory.

Mr Sanders’ campaign had got “at least 80 per cent of what we want”, his then policy director boasted at the time.

Likewise, it was not entirely vainglorious for Mr Sanders to declare last week that he had “won the ideological debate” in the Democratic party. As the left-leaning New York Times columnist Jamelle Bouie argued last week, the “two Sanders campaigns have, over five years, pulled the centre of the Democratic Party as far left as it’s been since before Ronald Reagan”.

Indeed, each of the moderate candidates in the Democratic primary race — not just Mr Biden, but Pete Buttigieg and Amy Klobuchar, too —staked out positions to the left of the party’s most recent nominees, including Barack Obama. 

The alleged champion of the “billionaire class” — Michael Bloomberg — even proposed a surtax on those earning more than $5m a year, while Mr Biden proposes tax increases double those advocated by Mrs Clinton.

But that legacy will all be for nothing if Mr Trump is able to eke out another narrow victory in the electoral college in November. As they did four years ago, the Vermont senator’s supporters could prove critical in tight race. Bill Clinton’s former pollster, Stan Greenberg, estimates that 30 per cent of Sanders voters are not currently guaranteed to vote for the Democratic nominee.

Mr Biden’s tributes to the “remarkable passion and tenacity” of his rival and his supporters –— and his appeals to Mr Sanders’ base of young voters — shows his campaign is well aware of the potential danger.

His actions in the coming days and weeks will decide whether he also receives credit for helping to defeat Mr Trump — or blame for helping to re-elect him.