How is British politics like a bad night at the theatre? Well, the leads are hopelessly miscast, the speeches go on too long and the minor roles are crude stereotypes. (I’m not buying this “Jacob Rees-Mogg” character, sorry.) And there’s another echo, too, which the playwright Lucy Prebble identified on 28 March. “I wonder if one of the reasons we get sick of certain issues is directly related to the lack of meaningful consequence,” she tweeted. “It’s like being stuck in an endless Act Two. Eventually, you resent whoever made you sit through the show.”

It’s a strange paradox: we live in a world where Amazon tries to deliver your package almost before you’ve bought it, while the entirety of the world’s knowledge lives inside a black rectangle you keep in your pocket. Yet politics seems crushingly static. We pull the metaphorical flush handle, again and again, but nothing happens.

The White House has a higher staff turnover than a medieval plague hospital, yet Donald Trump remains president. The glacial pace of the Brexit negotiations makes Waiting For Godot look like an airport thriller. And instead of drafting legislation, the government seems to be avoiding scrutiny by turning off the lights and pretending to be out.

To Jeremy Corbyn, that would be a familiar gambit. He has perfected the art of looking like a passenger in his own party, carried along by circumstance, waving graciously like a monarch from the carriage window. Last week’s fallout from his Facebook comment defending an antisemitic mural was no exception. Some of his supporters applaud his reluctance to engage, because they sense a plot (Blairite or Zionist, take your pick) to damage him before the local elections in May. “This whole row is being stirred up to attack Jeremy, as we all know,” wrote Momentum’s Christine Shawcroft in a public Facebook post on 30 March.

Although Labour’s strong election performance was supposed to have ended its civil war, this narrative of St Jeremy of the Sorrows – assailed by his enemies, suffering for our sins – is never far from the surface. It colours everything. A YouGov poll of Labour members found that 47% believed antisemitism was a genuine problem, but that it had been exaggerated to damage Corbyn “or stifle criticism of Israel”. A further 30% didn’t believe it was a “serious problem at all”. The remaining group, who are deeply concerned and believe the party needs to take urgent action, were far more likely to have voted for Owen Smith than Corbyn as leader in 2016.

That divide explains why the current row feels so intractable. Loyalists from Momentum and the pro-Corbyn trade unions now dominate the party’s Southside headquarters and its ruling national executive committee, but the turnover among local councillors has been slower. At the grassroots, then, there are still frequent clashes between Labour’s new membership and its old guard. Everything is a proxy war. Admittedly, for the conspiracy-minded, it must seem strange that a Facebook comment made by Jeremy Corbyn in 2012 is being debated six years later. Talk to Jewish Labour members and community leaders, however, and the opposite view emerges: they are surprised it has taken this long. The Jewish Chronicle first asked Corbyn about his defence of the mural, which depicted big-nosed bankers counting money, in 2015. The newspaper did not receive an answer.

Corbyn now says that he did not see the mural properly before commenting on it. Another dramatic concept is useful here: the unreliable narrator. When Corbyn pledges zero tolerance, he wants to be taken at his word. The trouble is, for many in the Jewish community, his words are worthless. There is a disconnect between the Labour’s leader sweeping statements about opposing racism and the reluctance to act against his friends and allies. As a politician, Corbyn is loyal to a fault and here the fault is clear: excusing antisemitism.

This crisis has been building for months. The Chakrabarti report was supposed to show that the leadership was taking antisemitism seriously, but its “independent” author joined the shadow cabinet soon after its publication. At the report’s launch, Corbyn was filmed chatting happily to an activist who had handed out leaflets calling his MPs “traitors”. One Jewish MP left in tears. Pressure has also been building in constituencies where Jewish councillors and members have been accused of disloyalty for complaining about antisemitism. Ultimately, it was the intervention of backbench Labour MP Luciana Berger, who tweeted that she had asked Corbyn’s office for comment on the mural, which made his continuing silence untenable. An open letter defending Corbyn on Facebook last week, which attracted 2,000 likes, began by suggesting that the Labour leader must feel “battered, bruised and damn near hopeless and helpless”. Those adjectives could also be applied to Berger, who has seen three men jailed for racist threats against her. “Hitler was right,” read one of their comments, alongside a picture of the MP with a Star of David on her forehead. “You better watch your back Jewish scum,” read another. The third called her an “evil money-grabber” and Photoshopped her face on to a rat.

If you don’t know about this back story, but do know about the “relentless attacks” on Corbyn so often referred to by his supporters, ask yourself why. The brutal and hysterical campaign against him in the rightwing press has, in the words of one critic, turned him into “the eternal victim”. It has become an excuse to dismiss all criticism as illegitimate. But there are other victims.

Facebook Twitter Pinterest Labour MP Luciana Berger addresses a demonstration against antisemitism in the party in Parliament Square. Photograph: Jack Taylor/Getty Images

The hate spewed at Berger is the inevitable consequence of indulging antisemitic tropes about global elites, cabals and conspiracies. It is unsurprising that her colleagues find it deeply offensive to suggest her only motivation is wounding Corbyn. At the meeting of the parliamentary Labour party on Monday, which the leader did not attend, Berger had sharp words for fellow MPs who sent her messages of support in private, but stayed silent in public. She didn’t want their sympathy, she said, but their help. That appears to have pricked some consciences. On Thursday, 39 MPs, including shadow ministers, signed a letter demanding the removal of Christine Shawcroft from the NEC.

What happens next? Act Three is supposed to bring a resolution – and possibly catharsis. In the classic “hero’s journey”, the protagonist might learn something about himself and use this knowledge to resolve his original problem. But sceptical Labour MPs believe their leader still has not grasped the importance of actively confronting antisemitism on the left. Of an email sent to party members, one said: “It was not at all bad, but a week too late.”

The next meeting of the parliamentary party is scheduled for the first Monday after the Easter recess and Corbyn is due to attend. The day afterwards, the Tories have opportunistically called a Commons debate on antisemitism. Unless Corbyn and the NEC can show they have a grip on the problem, some MPs say they are prepared to use parliamentary privilege to name those who haven’t done enough to combat antisemitism, “including fellow MPs and members of the NEC”. It is also hoped that the NEC can be persuaded to give up its role in dealing with complaints, in favour of a truly independent process. The most pessimistic backbenchers see Corbyn’s inability to take responsibility for the situation as evidence of a wider tendency to dodge tough decisions. “This is the difference between being a backbencher for 30 years and being a leader,” says one. He has enviable control of the party machinery, notes another, “so why does he always act like he has no power?”

What did last week reveal about the state of Labour? That Corbyn’s strengths as a speaker are matched by his weakness as an actor. That some supporters believe any criticism must be motivated by jealousy, disloyalty or factionalism. And that there is no appetite for a breakaway party or another doomed attempt to topple him.

So yes, Labour is trapped in an endless Act Two. But despite Corbyn’s martyred demeanour – and, whenever the subject is anything other than Brexit, his insistence that he is merely the voice of the membership – he is the party’s leader. Who is the protagonist in this drama, if not him? If Labour’s current story is going to reach a satisfying conclusion, only he can move the plot forward.

• Helen Lewis is deputy editor of the New Statesman