But both delegate maths and the mounting public impatience of senior Democrats at Mr Sanders’ seeming unwillingness to clear the field eventually forced his hand.
Unlike 2016, when he fought Hillary Clinton long after it was clear she had won, Mr Sanders this week formally endorsed Mr Biden.
In a joint, live-streamed event the Vermont senator said: “We need you in the White House. I will do all that I can to see that that happens, Joe.” Mr Biden, in turn, pledged “one of the most progressive administrations” since Franklin Roosevelt 90 years ago.
Mr Sanders’ move allows Barack Obama’s loyal deputy to effectively clinch the Democrat nomination earlier in the primary season than any of his predecessors in the last 16 years.
But Mr Biden is acutely aware that, while Mr Sanders may now be out of the race, the battle to win over his supporters, some 12 per cent of whom voted for Mr Trump four years ago, is not yet over.
This week, he moved to shore-up the backing of Sanders supporters, Mr Biden pledged debt write-offs for students and an expansion of the Medicare health programme, two signature Sanders policies.
If Mr Biden has justifiable anxieties about how — or whether — some of the most ardent “Sandernistas” may cast their ballots in November, his campaign will have less worries about the so-called “kosher vote”.
Polling carried out by the Pew Research Centre in January found that, alongside African-Americans, Mr Sanders significantly underperformed against Mr Biden among Jewish Democrats.
Numerically relatively small, Jewish voters are also concentrated in states such as California, New York and New Jersey which overwhelmingly vote Democrat.
Nonetheless, Jews as a percentage of the adult population are above the national average in two key swing states: Florida, which has produced some nail-bitingly close results, and Pennsylvania, which Mr Trump won by less than a single percentage point in 2016.
There’s also the potential for the small but not insignificant kosher vote to play a role in four other battleground states: Arizona and Nevada in the south-west, and Michigan and Minnesota in the Midwest.
In the fight against the president for Jewish votes, Mr Biden is well-placed. Continuing a long historic pattern, Mrs Clinton won the votes of over 70 per cent of Jewish voters in 2016.
Mr Trump, by contrast, was backed by less than a quarter of Jews, losing even the small gains of the 2012 Republican presidential contender, Mitt Romney.
There is, moreover, little sign that Mr Trump has improved his standing among Jews since he entered the White House.
Polling last September found that, at 29 per cent, the president’s approval rating among Jews was at the same level as in January 2017 and well below the somewhat anaemic 42 per cent he registered with voters overall at the time.
Nearly two-thirds of Jewish voters said they identify with the Democrats; a figure again unchanged since Mr Trump took office.
Despite skewing heavily to the left, Jews thus share a trait with many fellow Americans: whether they love or hate him, few have changed their minds in four years about the most polarising president of modern times.
