On one point I agree with his opponents: Jeremy Corbyn has little chance of winning the 2020 general election. But the same applies to the other three candidates. Either Labour must win back the seats it once held in Scotland (surely impossible without veering to the left) or it must beat the Conservatives by 12 points in England and Wales to form an overall majority. The impending boundary changes could mean that it has to win back 106 seats. If you think that is likely, I respectfully suggest that you are living in a dreamworld.

In fact, in this contest of improbabilities, Corbyn might stand the better chance. Only a disruptive political movement, that can ignite, mesmerise and mobilise, that can raise an army of volunteers – as the SNP did in Scotland – could smash the political concrete.

To imagine that Labour could overcome such odds by becoming bland, blurred and craven is to succumb to thinking that is simultaneously magical and despairing. Such dreamers argue that Labour has to recapture the middle ground. But there is no such place; no fixed political geography. The middle ground is a magic mountain that retreats as you approach. The more you chase it from the left, the further to the right it moves.

As the social philosopher Karl Polanyi pointed out towards the end of the second world war, when politics offers little choice and little prospect of solving their problems, people seek extreme solutions. Labour’s inability to provide a loud and proud alternative to Conservative policies explains why so much of its base switched to Ukip at the last election. Corbyn’s political clarity explains why the same people are flocking back to him.

Are they returning because he has tailored his policies to appeal to the hard right? Certainly not. They are returning because he stands for something, something that could help them, something that was not devised by a row of spadbot mannikins in suits, consulting their clipboards on Douglas Alexander’s sofa.

Nothing was more politically inept than Labour’s attempt before the election to win back Ukip supporters by hardening its stance on immigration. Why vote for the echo when you can vote for the shout? What is attractive about a party prepared to abandon its core values for the prospect of electoral gain? What is inspiring about a party that grovels, offering itself as a political doormat for any powerful interest or passing fad to wipe its feet on?

In an openDemocracy article, Ian Sinclair compares Labour’s attempts to stop Corbyn with those by the Tories in 1974-75 to stop Margaret Thatcher. Divisive, hated by the press, seen by her own party as an extremist, she was widely dismissed as unelectable. The Tory establishment, convinced that the party could win only from the centre, did everything it could to stop her.

Across three decades New Labour strategists have overlooked a crucial reality: politicians reinforce the values they espouse. The harder you try to win by adopting your opponents’ values, the more you legitimise and promote them, making your task – and that of your successors – more difficult. Tony Blair won three elections, but in doing so he made future Labour victories less likely. By adopting conservative values, conservative framing and conservative language, he shifted the nation to the right, even when he pursued leftwing policies such as the minimum wage, tax credits and freedom of information. You can sustain policies without values for a while but then, like plants without soil, the movement wilts and dies.

The Labour mainstream likes to pretend that Blair’s only breach of faith was the Iraq war. The marketisation of the NHS, the private finance initiative, the criminalisation of peaceful protest, collusion in the kidnap and torture of dissidents from other nations, the collapse of social housing – I could fill this page with a list of such capitulations to greed and tyranny. Blair’s purges, stripping all but courtiers from the lists of potential candidates, explain why the party now struggles to find anyone under 50 who looks like a leader.

The capitulations continued under Ed Miliband, who allowed the Conservative obsession with the deficit and austerity to frame Labour politics. As Paul Krugman explains, austerity is a con that does nothing but harm to the wealth of this nation. It has been discredited everywhere else: only in Britain do we cling to the myth. Yet Miliband walked willingly into the trap. His manifesto promised to “cut the deficit every year” and to adopt such cruel Tory policies as the household benefits cap.

You can choose, if you wish, to believe that this clapped-out, alienating politics – compounded by such gobsmacking acts of cowardice as the failure to oppose the welfare bill – can capture the mood of the nation, reverse Labour’s decline and secure an extra hundred seats. But please stop calling yourself a realist.

Rebuilding a political movement means espousing what is desirable, then finding ways to make it feasible. The hopeless realists propose the opposite. They assemble a threadbare list of policies they consider feasible, then seek to persuade us that this package is desirable. If they retain core values, they’ve become so muddled by tacking and triangulation as to be almost indecipherable.

So great has the damage been to a party lost for 21 years in Blair’s Bermuda triangulation that it might take many years until it becomes electable again. That is a frightening prospect, but the longer Labour keeps repeating the same mistakes – reinforcing the values it should be contesting – the further to the right it will push the nation, and the more remote its chances of election will become. The task is to rebuild the party’s values, reclaim the democratic debate, pull the centre back towards the left and change – as Clement Attlee and Thatcher did in different ways – the soul of the nation.

Because Labour’s immediate prospects are so remote, regardless of who wins this contest, the successful candidate is likely to be a caretaker, a curator of the future. His or her task must be to breathe life back into politics, to recharge democracy with choice, to ignite the hope that will make Labour electable again. Only one candidate proposes to do that.

*This article was originally titled: ‘Curator of the future’ and was published on the Guardian website on the 19th of August