Joe Biden is back. Following Super Tuesday, he is now the clear frontrunner to win the Democratic primary and face off against Donald Trump in November. But the race isn’t over yet, and the risk now is that a drawn-out and contentious primary could harm the party’s eventual nominee, be it Biden or progressive favorite Bernie Sanders. It is imperative that the process come to an end as soon as one candidate has a prohibitive lead, and that Democrats begin to unite around their nominee.

Tuesday night’s results make it look increasingly likely that Biden will be that nominee. Sanders’ victories were confined to the west and his home state of Vermont, with Biden notching up wins everywhere else. Sanders is in the lead in slow-counting California, but it appears that Biden won at least 15% of the vote, meaning he is above the viability threshold necessary to receive delegates and will eat into Sanders’ delegate haul there. Biden also prevailed in Texas, the other big prize of the night.

Sanders’ inability to land a killer blow on Super Tuesday matters because it was supposed to be his night. His strength among Latino voters – a set of communities in which he has invested enormous outreach and attention since 2016 – was meant to combine with his ability to turn out young progressives to deliver a resounding victory. And Sanders needed that victory because the states still to vote are demographically and ideologically less favorable to him, suggesting he will struggle to make up lost ground.

Perhaps the most disappointing ongoing story for Sanders is his inability to turn out the new voters on whom he has premised his whole theory of victory. There have been large increases in turnout in several primary states so far, but with the exception of Nevada the gains have largely accrued to Sanders’ opponents. In Virginia – a swing state – turnout nearly doubled compared to 2016, but Biden beat Sanders by a more than 2-1 margin. If Sanders cannot turn out new voters to make up for the moderates he alienates, it is clear he would lose badly against Trump in November.

What should Sanders do now? Luckily, his interests going forward align with those of the party – if only he can be persuaded to see it that way. So far, Sanders has failed to expand his appeal beyond the party’s left wing. His attempt to turn the primary into a referendum on “the Democratic establishment” has backfired, with many voters showing that they are more comfortable lining up behind “the establishment” than Sanders’ insurgency. If he has any chance of bouncing back, Sanders needs to quit the divisive rhetoric and begin appealing to different wings of the party. This would not only be strategically wise in the primary – it would also show the sort of flexibility required to win in November.

If he has any chance of bouncing back, Sanders needs to quit the divisive rhetoric and begin appealing to different wings of the party

Even if Sanders ultimately loses the primary, the beginning of a process of reconciliation will go a long way to helping Democrats beat Trump. Biden is a flawed candidate, and one of his main problems in November will be his difficulty convincing the left wing of the party to turn out to vote for him. For prominent leftwing figures to intensify rhetoric implying that the nomination is somehow being unfairly stolen from Sanders by “the establishment” is to recklessly endanger the party’s chances in November. If such rhetoric was a viable path to a Sanders’ candidacy and perhaps to victory against Trump, it was perhaps defensible. But it is clear that it no longer is.

What is instead required from the left right now is introspection. While the 2016 primary was plagued by concerns over bias at the Democratic National Committee and the role of superdelegates, in 2020 there are fewer scapegoats available. Blaming billionaires and “the establishment” for your losses doesn’t get you very far when the only billionaire left in the race is helping you by taking votes from your moderate opponent and you are drastically outspending everyone but the billionaire. Something else is going on here. Rather than lashing out, the left needs to look inward and think seriously about what that might be.

What might be happening is that there is a flaw in the theory of politics which has powered Sanders to date. As a result, both the candidate and his movement may have to readjust their understanding of political reality. It might mean accepting that they can only advance their goals through compromise and that a democratic system means that nobody gets everything that they want, and that they often get much less. The alternative – wilfully splitting the party and handing the keys to the White House back to Donald Trump in a fit of pique at losing the argument to Joe Biden – will appear petty, vindictive and obtuse.

Introspection is also needed from the other side. If Biden goes on to become the nominee, he desperately needs to signal that he recognizes the very legitimate critiques levelled at him by the left. He should acknowledge Sanders’ tremendous achievement in shifting the party to the left on a range of issues. Most of all, Biden will need a vice-presidential nominee who carries serious credibility with the younger and progressive voters he struggles most to connect with.

Avoiding a catastrophic fracturing of the party as the primary enters its most contentious phase is now more important than the success of any individual candidate. Measured, thoughtful actions from Sanders and his supporters in their time of disappointment will speak volumes about their character, enhance their chances of ultimately winning the primary, and keep the party competitive against Trump regardless of what happens. Scorching the earth will do the opposite. The party and the country is watching nervously to see what they do next.