Joe Biden’s victory over Bernie Sanders in the crucial Michigan primary saw him defeat the Vermont senator among critically important demographics – several of whom supported Mr Sanders over Hillary Clinton in 2016.

The exit polls showing the strength of Mr Biden's victory deal a serious blow to Mr Sanders’ claim that he is the candidate best placed to defeat Donald Trump, and leave Mr Biden almost certain to win the nomination less than two weeks after his stunning comeback in South Carolina.

Along with Wisconsin and Pennsylvania, which have yet to hold their primaries this year, Michigan was one of the three pivotal states Donald Trump peeled away from Hillary Clinton by razor-thin margins in 2016.

Any Democrat hoping to win the state back must be able to win a broader range of voters and drive turnout higher than she did. Mr Sanders has consistently argued that he can do just that, particularly since the Nevada caucuses, when there were signs he was broadening his coalition.

But at that point, Mr Sanders was facing a divided field of “moderates”. Now the field has narrowed to two men, Michigan’s exit polls show him falling short of his 2016 results while Mr Biden outperforms Ms Clinton.

The coalition of voters swinging to Mr Biden in Michigan includes not just black voters and women, both core Democratic constituencies where Mr Sanders been struggling, but also white men both with and without college degrees.

These men, who were crucial to Donald Trump’s victory in Michigan and elsewhere, turned out for Mr Sanders in the 2016 primary by a 15-point margin; this time around, they have deserted him for Mr Biden, albeit only narrowly.

Where Ms Clinton narrowly lost to Mr Sanders among white women (51-47), Mr Biden won them over by a comfortable 59-35 among those with college degrees and 55-42 among those without, according to the exit polls.

Mr Sanders’s most decisive margins came from the groups he has always been most associated with: voters under 29, where he defeated Mr Biden by 57 points, and those calling themselves “very liberal”, where he won by 33.

Mr Sanders did win by a hefty margin among Latino voters, following a pattern across the country, but they only made up around 6 per cent of the Michigan electorate.

The importance of building a wider coalition than Ms Clinton can hardly be overstated. According to the exit polls from November 2016, she lost Michigan’s overall male vote to Mr Trump by a margin of 12 per cent; she lost its white men 64-29 and its white women 51-43.

And while she won overwhelmingly among black voters, they turned out in fewer numbers across the country than in 2012, while white people – who broke for Mr Trump 57-36 – did the opposite.