Since the beginning Jeremy Corbyn has faced a die-hard band of parliamentary enemies who were not interested in his support from Labour party members, and took every chance to question his suitability to lead. It was, however, not this small gang of irreconcilables but 81% of his MPs, encompassing the mushy middle and the soft left as well as the right, who tonight supported a vote of no confidence in him. The question is thus no longer whether Mr Corbyn should continue to lead, but whether he is in fact any longer leading at all. The unavoidable answer is that he has ceased to do so, in any ordinary sense.

His few friends in parliament, and many grassroots supporters, have some legitimate complaints. They object that a move against him after the EU referendum loss is arbitrary punishment for what was, first and foremost, David Cameron’s defeat; punishment which, furthermore, is out of kilter with the public’s Brexit vote. They also resent the choreographing of so many shadow cabinet resignations to do maximum damage, and protest, too, that Mr Corbyn’s electoral record is better than is often said. He held his own in a run of byelections, most recently and impressively in Tooting, and avoided the wholesale blood-letting in the English councils that was widely predicted in May.

But there is no use pretending the Corbyn Labour party has been doing well enough. Its vote share in the local elections was down on Ed Miliband’s 2012 starting point, before Mr Miliband, lest we forget, went on to a shocking defeat. Mr Corbyn’s success in mobilising a new activist base, including many in a younger generation that is priced out of decent housing and saddled with insecure work, has not reconnected the party with those crumbling heartlands that broke so heavily for leave. His radical pitch was meant to get Labour back in the game in Scotland, but at Holyrood this year it sank even below 2015’s depths, and got beaten by the Tories.

Mr Corbyn was always isolated at Westminster, with at most 20 genuinely loyal MPs. But until the referendum he could run a half-functioning frontbench, because some sceptical colleagues were willing to give his experiment time. No longer. What’s changed is less Brexit itself than the sudden potential – despite Boris Johnson’s denials – for an early election.

A defiant Mr Corbyn tonight brushed off the thumbs-down that four in five colleagues gave him, by reciting the rulebook which puts the leadership decision in the hands of the members who he believes remain as loyal as ever, although – amid such chaos – can that be assumed? More fundamentally, the rulebook becomes immaterial when there is no ability to do the basic job. The rules of a charity may, for example, put the appointment of a chief executive in the hands of the trustees, but that chief executive will not be able to function if the staff all want him out. And in the Corbyn case, the option of replacing “the staff” does not exist without showing contempt to the electorate, since they are not mere party functionaries, but MPs elected by 9.3 million Labour voters. And if the election comes this year, there would be no time to go for wholesale reselections to pick a new slate of Corbynite candidates, even if Mr Corbyn had not solemnly promised to avoid this unwise course.

Mr Corbyn is thus saddled with trying to lead a team that wants him out, and the balance of forces is even more hostile than that which did for Iain Duncan Smith. The existential danger for Labour is that the pivot which has defined it for a century – the pivot between the voluntary and parliamentary wings – would come unstuck if Mr Corbyn clings to his leadership of the former after his leadership of the latter has collapsed. That cannot be allowed to happen. But nor should Mr Corbyn’s supporters be asked to fold without some reassurance about what happens next. His victory last year reflected deep discontent with New Labour’s economic and foreign policies. The national executive committee, which is evenly balanced between Labour’s right and left factions, must ensure the next leader builds a broad team that includes the long-neglected left. It must guarantee, too, a more open policymaking process, with franker debate than New Labour allowed. The Corbyn experiment is effectively over at Westminster, but in these ways it could still bequeath a useful legacy.