For political junkies, last week’s debates between the candidates fighting to become the Democratic party’s presidential candidate were a veritable feast.

So many Democrats — more than 20 in all — are competing for the right to take on Donald Trump next autumn that the first debates of the election season were spread across two nights.

Thanks to the luck of the draw, Bernie Sanders, the Jewish hero of the American left whose quixotic campaign for the Democrat nomination four years ago nearly upended that of Hillary Clinton, found himself in the second night’s contest, facing off against the frontrunner Joe Biden.

Ever since the former Vice President entered the race in April, Mr Sanders has been firing none-too-subtle shots at him, urging the party to avoid the perils of the “middle-ground”. Those attacks, pitching his radicalism against the perceived mushy centrism of the Washington veteran, consciously echo those which served the senator so well against 
Mrs Clinton.

But Mr Sanders found himself eclipsed. The much-anticipated confrontation with Mr Biden turned into something of a sideshow. Instead, it was California Senator Kamala Harris’s attacks on his civil rights record which left President Obama’s second-in-command battered and bruised.

It was a strong showing for Ms Harris, who is not Jewish herself but did smah a glass to celebrate husband Douglas Emhoff’s Jewish heritage at their 2014 wedding.

For Mr Sanders, the debates capped a difficult month. Four years ago, the self-proclaimed democratic socialist was largely alone against Mrs Clinton. The lack of alternatives allowed Mr Sanders to simultaneously play the roles of standard-bearer of the left, plucky underdog and principal challenger to the Democratic establishment’s pick for the presidency.

Ms Harris has snatched the last of those roles from him last Thursday, possibly only temporarily. One poll released after the debate even showed Mr Sanders — who has consistently run second to Mr Biden — dropping to fourth place as the California senator surged to within five points of the former vice president.

Nor can Mr Sanders any longer paint himself as the underdog. Since 2016, he has emerged as a powerbroker atop a formidable political machine. Instead it is the rise of South Bend mayor Pete Buttigieg, young and openly gay, which has captured the imagination of many younger Democrats.

But it is Massachusetts Senator Elizabeth Warren, a long-time friend and close political ally, who is proving Mr Sanders’s biggest headache. She appeared in the first of the two Democrat debates and, unlike Mr Sanders, dominated proceedings.

The two candidates are locked in what Time magazine has termed a “shadow primary” for the votes of progressive Democrats. Ms Warren has slowly advanced in the polls in recent weeks and the Real Clear Politics average has her nipping at Mr Sanders’s heels both nationally and in key early primary states.

In response to her policy-rich campaign, Mr Sanders last month unveiled a plan to write-off all $1.6 trillion (£1.2 trillion) of student loan debt, a proposal designed to both complement his eye-catching 2016 pledge to make college tuition free and outflank Ms Warren’s more modest proposals.

Mr Sanders pulled no punches against Mrs Clinton in 2016 — teeing up many of the attacks Mr Trump subsequently made upon her, critics say — but he has to tred more cautiously against Ms Warren. The two are competing for many of the same voters.

Indeed, the negative reaction to his dismissive suggestion that her rise was because voters want to “see a woman elected”, and his bungled effort to portray the fiery senator as part of the Democratic party’s “corporate wing”, show the potential dangers.

Perhaps Mr Sanders’ greatest problem is simple. In 2016, he had that precious political commodity: novelty. It is an attribute not available to the Vermont senator on his second shot for the presidency.