“Lisa smashed it, Jess smashed it”. To follow the Parliamentary Labour Party leadership hustings via WhatsApp you would think it’s just a question of who smashes it the most, and most often. In fact, the only question that really matters is: “who gets it?”

Who understands that, after four general election defeats for Labour in a row, something fundamental has changed in the dynamic of British politics, requiring the left project to be redefined and a new alliance of progressive forces to be formed?

Labour lost around 800,000 Leave voters to the Tories over Brexit and – in a way that shocked everyone – another 300,000 Remain voters to the Tories simply over mistrust of Jeremy Corbyn alone. It lost, in addition, around 1.1 million Remain voters to the Liberal Democrats, the Greens and the SNP. It won the youth vote, but massively lost among the elderly, and in the process sacrificed large majorities in its traditional heartlands. No matter who “smashed it” at the PLP hustings, understanding why these tectonic shifts are happening is the main task.

If you step back from the result, and look at the polling averages from May 2019 onwards, the reasons become clear. Britain's party system is fragmented. There are four forces: ex-Ukip right-wing nativists, mainstream conservatives, Labour progressives, and non-Labour progressives. In December, a coalition of mainstream Tories and overt nativists beat a left divided between Labour, the Lib Dems, the Greens and cosmopolitan nationalism. And they will do so in every election from now until the baby boomer generation is dead, unless the progressive half of Britain can form some kind of alliance.

Only if the incoming leader has a brain, and an advisory team, prepared to grapple with this new political reality does the left in Britain stand a chance of coming back in 2024. Yet Labour’s leadership battle is already becoming a tawdry parade of personal attributes and naff slogans. I admit, in the age of populism and a dumb media, that the personality of the leader is more important than in the age of John Smith, but even more important is whether they understand the world around them.

In Leigh, which went Liberal at the earliest opportunity (1885) and Labour at the earliest opportunity (1922) we saw a 9,554 majority overturned by the Tories through sheer nativist sentiment among older and retired workers. The MP was decent, the campaign slow and under-resourced – but the Tories barely needed to show their faces. On the Saturday before the vote in Leigh’s main shopping street, I argued with a 50-year old man in a bobble hat who wanted Boris Johnson to lock up Romanian migrants, and their children, and forcibly deport them overnight, the day after the election.

Labour lost, not because it could not argue with that man – my comrades and I argued patiently, for many minutes with him, in the freezing cold – but because it does not understand the world that produced him. It is a world dominated by three crises: an economic model that doesn't deliver for most people; a planet facing environmental catastrophe; and severe inequalities of technological power and control which make it impossible for the man in the bobble hat to know who is manipulating the information on which his racist mind-garbage was based.

Does Labour have answers to the crisis? On the climate crisis, the answer is yes. Corbyn's most significant legacy to Labour was his ability to oversee a transition to climate radicalism: the 2017 manifesto barely mentioned climate; the 2019 fiscal and industrial policy was entirely constructed around it. The question here is whether it can persuade ordinary people that its answers matter.

As for an alternative to neoliberalism, John McDonnell designed it. The 2019 manifesto, with its commitments to long-term borrowing, new targets for the Bank of England, and dramatic redistribution via the tax system, should remain the blueprint for future Labour manifestos.

However, here again, the manifesto bombed. Richard Tawney, after the 1931 election debacle, warned against Labour manifestos that became “a glittering forest of Christmas trees with presents for everyone” – but nobody had bothered to read Tawney.

Labour's correct and principled answers over climate and austerity bombed because the nativist narrative was coherent, clear and emotionally grounded. Against it, Labour had nothing effective. Until this changes – i.e. until Labour can come up with an economic and cultural offer to small town, low-skilled, Britain strong enough to drown out nativism – its clear task is to solidify the progressive majority of voters around a project.

Who gets this? By a head and shoulders the answer is Clive Lewis. He has attacked “Labourism” – i.e. party sectarianism and the “one more heave” it always produces. He has floated the idea of an electoral alliance in 2024 around proportional representation and House of Lords reform, and called for an open, internationalist left leadership. At the time of writing, he has just two backers out of the 202 Labour MPs. Unless something drastic changes, he will not be on the ballot paper.

Who doesn’t get it? The candidates at opposite ends of the political spectrum: Jess Phillips and Rebecca Long-Bailey. Whatever she says in public, it has been transparent for months that Phillips is the representative of the Blairite right: her project is to expel the left and reconsolidate neoliberal control over Labour behind a mask of folksy egotism.

Long-Bailey is clearly struggling with her core backers – the pro-Brexit union bureaucrats of Unite and the Communication Workers Union and the Lexiteer grassroots who would have preferred Ian Lavery to stand instead. More importantly, she is struggling with the legacy of, and backing of Corbyn and his team.

I do not believe Corbyn’s advisors bear primary responsibility for the defeat: Corbyn himself chose them. It was Corbyn who empowered them to impose some wholly unsuitable parliamentary candidates, turn the conference into a leadership rally and launch an ill-advised coup against Tom Watson. It was Corbyn whose failure to prepare for the Andrew Neil interview left him floundering; it was Corbyn who failed to heed advice to sign up to the IHRA definition of anti-Semitism; it was Corbyn who could not find the presentational resources to lay a finger on Johnson during the entire campaign.

For Long-Bailey to claim, as she did this week, that Corbyn was a “ten out of ten” leader beggars belief. No matter how distant she now wants to be from Corbyn on anti-Semitism, or Brexit, the fact is her campaign represents continuity with ideas and methods that failed. And with a bureaucratic machine politics just as damaging as that of the Blair/Brown years. If Long-Bailey showed any signs of a platform or political method independent from the Unite machine that has backed her, it would be a different matter. Maybe she will.

But failing that, if Lewis cannot make the ballot, the left’s way forward is to back Keir Starmer as leader. The internationalist left should build something independent, which I hope Starmer will listen to and protect. But we should unite the party around a project of radical social democracy. To be clear, that means assembling a shadow cabinet as broad as possible, including Lisa Nandy and her Blue Labour backers from the right of the party, and managing the political differences through argument, not diktat.

You can criticise Starmer for many things: the compromises he made as director of public prosecutions and his resignation during the chicken coup. But you cannot say he is not left wing. From the miners and print workers’ strikes onwards, even if you leave aside co-editing a Trotskyist front magazine in his 20s, Starmer has been of the humanist and socially-liberal left. As someone who stood in the way of the same mounted police charge as he did, at Wapping in 1986, I can tell you it didn't feel very centrist at the time.

In an era where personality matters, Starmer has a lot going for him. The raw 12 minutes he spent bossing Andrew Marr in the studio last Sunday felt like a revelation after the months we've spent wincing during Corbyn’s live appearances. He also connects with working-class people better than Corbyn did – though that is not a differentiator in this contest: all of the candidates do. By this I mean real, undecided or hostile voters, not the bussed-in faithful at Labour Roots rallies.

Finally, Starmer has worked and lived in the world of professional competence. Corbyn surrounded himself with amateurs: strategists who didn't care about the polls, office managers who could not manage.

Professionalism means, above all, understanding what you do not know; listening to expertise; absorbing complicated briefs quickly; building networks of influence, not bureaucratic command structures. Yes, it comes with an overhead cost of overcaution, or potential openness to corporate influence, but with a democratically-run party those dangers can be fought.

What matters now is the membership. Do they get it? Or will they cling, out of desire for moral comfort, to a form of 20th-century leftism that sounds good in the pages of Tribune but can only guarantee another decade of defeat?