Jeremy Corbyn’s support among Labour members has collapsed, according to polling for the Times: nearly two-fifths of them would like to see the leader step down before the next general election; 43% say he’s doing a bad job; more than 70% see antisemitism as a genuine problem; and 27% want the leader to stand down immediately.

But one man’s collapse is another’s resounding mandate, and the leadership is apparently taking solace from the fact that three-fifths of the members are still supportive. The 56% continuing to back Corbyn into the next battle is not a vast reduction from the 61.8% who supported him against Owen Smith’s challenge in 2016. From this perspective, the leader retains the force field he’s had since his first election a year before that. The parliamentary party can rebel, and the mainstream media cavil all they like, but with the members on his side, Corbyn is unassailable.

Corbyn’s leadership is more animated by its discontinuity with old New Labour than by its opposition to the Tories

This could go backwards and forwards for ever, like an executive toy: many of the members who would once have supported Smith have now left the party, driven away by its Brexit stance, its reaction to antisemitism or a more amorphous sense of hopelessness at the unfocused opposition Labour presents to the darkest and most destructive Conservative party in living memory. Membership has declined by 10% since its 2017 high. Labour, again, takes reasonable comfort from the fact it remains, at more than half a million, by far the largest political party in Britain and among the biggest progressive membership organisations in Europe. Yet even if we take it as read that the 10% who have left were the most lukewarm, it would be optimistic indeed to believe the fierce personal loyalty that characterised the party for the first flush of Corbyn’s leadership can still be relied upon.

The problem is Brexit but not just Brexit; the problem is antisemitism but not just antisemitism. Functionally, these problems can both be distilled in the reservations that those who supported the Corbyn project, but not the Corbyn personality, had from the start. Corbyn and his allies made it a point of honour to ignore not just the mainstream media but also the opinion polls. This made sense when the polls were (with a few honourable exceptions) wildly unenlightening and the media (again, with exceptions) indefensibly credulous. Yet the leadership remains wedded to the idea that negative polling can be dismissed as an establishment plot, and stolidly resists any data that goes against a precast narrative.

Liberal Democrat and remain supporters led by the MP Ed Davey, centre, march in London against Brexit. Photograph: Wiktor Szymanowicz/Rex/Shutterstock

The typical leave voter is characterised in Labour’s strategy as a working-class northerner with deep and justified objections to the EU. This has been shown again and again – from the left (Danny Dorling) to the centre (Peter Kellner) – to be untrue. Only one in eight leave voters met that description. There is seemingly no amount of data, from any source, that can undermine this totally false dichotomy between the authentic, angry, Brexity north, which is Labour’s true heartland, and the pampered, chattering, remainey south, which Labour is apparently happy to take or leave.

Huge amounts of work have been done on the bizarre new political alignment, where Labour is polling 24% on a good day and lags behind the Liberal Democrats on a bad one. To the extent that these numbers are taken seriously by the leadership at all, it is only to celebrate the fact that they could, with a fair wind, deliver a progressive government by coalition. Yet there is a huge amount of jeopardy in that stance: with a less fair wind, a couple of percentage points either way, Labour could be reduced to the third or even fourth party.

Direct accusations from the media, meanwhile, have always fallen into the same category of “things that can safely be ignored”. Statements from the past about the IRA, sharing platforms with terrorists, laying wreaths upon graves of contested occupancy – these were dredged up instrumentally, with hand-wringing so exaggerated it was a pantomime, and cut no ice with voters two years ago (as Anthony Lane memorably described in his Old Testament post-GE analysis for the New Yorker, “And the elders spake again, and said to the young people, Beware, for he gave succour in days of yore to the I.R.A. And the young people said, ‘The what?’”). But antisemitism was in a different category: the situation should have been examined on its own merits, but instead passed into a playbook. “What happened last time? We ignored it and it went away.”

Corbyn’s leadership has always been more animated by its insistent discontinuity with old New Labour than by its opposition to the Conservatives, which it took as read: at the start, that created a driving sense of purpose, originality and hope. To oppose austerity was necessary but boring: the far more interesting question was, what were the structural economic and cultural conditions that had given rise to it?

Yet this magnetic attraction to Labour internecine conflict has been superseded by events. Boris Johnson, a man who will abandon all decency for an Atlanticist fantasy of which chlorinated chicken is the least bad consequence, is a more important foe than Alastair Campbell. He is a more important foe than Tony Blair. This has to be taken seriously.

The interiority of the Labour leadership, the fogginess of its position, its stubbornness; all these things drag on its popularity, and all are analysed either in terms of its personalities, or the battle between Stalinists and Trotskyists – factions only sketchily understood even from within, and more intractable the better you understand them. But from only a fractionally different angle this can look more practical than ideological, and consequently easier to shift. The assumptions that were reasonable, and successful, at the start have hardened into talismans, like the lucky pants of an athlete. They are unequal to the current crisis.