Bliss is fleeting. The Labour leadership returned to Westminster after the Easter break, having dominated the recess with a series of eye-catching economic policy announcements. The best of these, such as a £10 minimum wage and free meals for primary school children, unified the party’s fractious tribes and sent a clear message about the kind of country Jeremy Corbyn wants to build. As a Labour source puts it, this is one “where we take from those with the most to do something for everybody”.

But although the policies are popular, the party and its leader are not. Labour consistently scores in the mid-to-low 20s in the polls, while the percentage of people who say that Corbyn would be a better prime minister than Theresa May hovers in the mid-teens. That points to the kind of election result seen across Europe in the past decade: the disintegration of the main party of the centre left and triumph for the centre right.

Optimists in Team Corbyn think that they might still win. Looking across the Channel, where Jean-Luc Mélenchon, the leftist candidate for the French presidency, has surged in the polls, they believe that the televised debates could give Corbyn a second chance to make a first impression. “We forget that actually Jeremy didn’t start out where he is now among Labour members,” one frontbencher says. “But in that Question Time-style arena, he knows what he thinks, and he says it in a warm and friendly way. Whereas Theresa May, she doesn’t think on her feet. She hasn’t been tested in that arena.” Yet there is a problem: Downing Street has ruled out a repeat of the televised debates. (Labour sources note that David Cameron did the same before bowing to pressure from the other parties.)

This rosy view does not extend even to the outer limits of the leader’s circle, however. Along with the Corbyn sceptics who make up the majority of the parliamentary party and about a third of the grass roots, some close to Corbyn believe that his radical past and his shaky start will prevent the public from ever warming to him, gruffly charming though he may be on Loose Women.

So why do the “soft Corbynites” hang on? As with Labour members – who are more aware of Corbyn’s defects than their caricature in much of the media suggests – they fear what will come after him. Many in the grass roots fear a sharp turn to the right on immigration and welfare spending, while Corbynites at Westminster fear that his successor will purge the Labour left entirely.

For them, the next election is not about winning over the public but survival within the party. If Corbyn’s performance on the campaign trail is stronger than expected, they say, he can stay on as leader. The argument will be that the contest came at a time of his opponent’s choosing, and that Neil Kinnock was given an second crack at the electorate after a landslide defeat in 1987.

Whether they succeed depends on a series of unknowns. If Team Corbyn can force May to U-turn on televised debates and if he puts in a bravura performance, perhaps he can get a hearing. Equally, if the campaign is dominated by unhelpful interventions from Labour grandees, the argument that Corbyn has not been given a fair chance may find support among party members.

To MPs who oppose Corbyn, this early election is a gift – at least, to those who retain their seats in what is likely to be a shrunken parliamentary party. Late last summer, when speculation was rife that May would seek an early election, the ruling National Executive Committee gave itself sweeping powers over parliamentary selections. Any standing Labour MP who wishes to run again will be waved through without selection, as will any defeated parliamentary candidate from 2015 who fancies another shot in the same seat. Crucially, those MPs and candidates were selected by a party not yet transformed by its Corbyn-era membership surges. A hard-left takeover of the parliamentary party will therefore remain some distance away.

Meanwhile, centre-left MPs who were planning to retire in 2020 are being quietly urged to hang on and prevent the left from gaining a further foothold. That is why Harriet Harman was so quick to announce that she will stand for a ninth term in parliament.

The demands of an election campaign will ensure that Labour, a party never particularly sold on internal democracy, will now resolve many of its most divisive disputes by fiat. Where a seat falls vacant, the shortlist will be controlled by the national executive's commitee's officers, which means the biggest winners will likely be trade union officials from the party's centre.

The election also threatens the “McDonnell amendment”, which would reduce the threshold needed to nominate a candidate for the leadership from 15 to 5 per cent of MPs and MEPs. This was expected to be debated at party conference in the autumn and was considered a key demand of the Corbyn faction in any succession planning. Now, any local party that has not yet chosen its conference delegates will have them chosen by its constituency executives, who are also largely drawn from the party’s Corbyn-sceptic wing. This suggests that the amendment will not pass – and that any future candidate from the left would, like Corbyn, be reliant on the kindness of strangers. After 2015, the gift of nominations to “broaden the debate” will no longer be forthcoming.

Labour will fight two campaigns over the coming weeks. The leader’s optimistic allies will fight a campaign to win power at Westminster, but his more pessimistic supporters and his opponents will fight another: to convince the party membership that the expected defeat is not their fault.