It is sometimes said about the Democratic party that were its members asked to form a firing squad, they would stand in a circle. 

This month, it was Hillary Clinton’s turn to unload, firing a series of salvos at the man she defeated in last year’s Democratic primaries. According to Mrs Clinton’s recently-published account of the 2016 election, titled What Happened, Senator Bernie Sanders aided and abetted Donald Trump in pulling off the biggest political upset in modern US history. 

Accusing him of “innuendo and impugning my character”, Mrs Clinton suggests that Mr Sanders’ attacks “caused lasting damage, making it harder to unify progressives in the general election and paving the way for Trump’s ‘Crooked Hillary’ campaign”. She takes issue, too, with Mr Sanders’ supporters — “the so-called Bernie Bros” — for “harassing” her supporters online, while also noting that the Vermont senator is an independent who has long refused to join the Democrats. “He didn’t get into the race to make sure a Democrat won the White House, he got in to disrupt the Democratic Party,” she writes.

Mr Sanders, whose strong run in 2016 made him the most electorally successful Jewish presidential candidate, was typically dismissive of Mrs Clinton. He said that, having lost against “the most unpopular candidate in the history of [the] country” she was “understandably upset”. 

But while her detractors accuse Mrs Clinton of “relitigating” the 2016 election, the real battle between the two former opponents is about the future. As the New Yorker commented recently, while Mr Sanders’ presidential race formally ended last summer “his campaign never did”. The Vermont senator has established a national political organisation, Our Revolution, maintained a high media profile, and has repeatedly criss-crossed the country, visiting key electoral states. Over the summer he made a number of trips to New Hampshire and Iowa, the much-watched first states to vote in the 2020 primaries. 

Neither this activity, nor Mr Sanders’ refusal to rule out running in 2020, has escaped the attention of the Washington press corps. Early polls suggest he leads the race for the Democratic nomination, comfortably beating former Vice President Joe Biden, among others. 

Mr Sanders continues to rail against the “resistance of the Democratic establishment” to his plans and insists that he remains an independent. However, A Better Deal, the Democrats’ manifesto for the 2018 congressional elections, is infused with Mr Sanders’ economic populism.

Mr Sanders is skilfully tapping the anger many Democrats feel in the face of Mr Trump’s hard-right political agenda. However, as some commentators have noted, he remains, as he was throughout last year’s race, reticent to speak about his Jewish identity. 

At an event in New York earlier this month, for instance, Mr Sanders reportedly omitted mentioning Jews and antisemitism as he attacked the “oppression and suffering” facing many Americans under Mr Trump. 

In the wake of the sharp rise in antisemitic attacks that have  accompanied Mr Trump’s arrival in the White House, the events of Charlottesville last month, and the president’s apparent inability to unequivocally condemn neo-Nazis, Mr Sanders’ behaviour may appear strange. In some regards, however, it perhaps reflects a criticism strongly hinted at by Mrs Clinton: that Mr Sanders’ emphasis on class and economics sometimes appears to blind him to questions of identity.

Mr Sanders, who would enter the White House at 78 if ran and won in 2020, may ultimately decide to sit the race out. 

His current campaign, moreover, is designed to ensure that, whether he is at the helm or not the Democratic party moves decisively to the left with the elimination of the last vestiges of the business-friendly centrism associated with both Bill and Hillary Clinton.