The running joke about Jeremy Corbyn’s leadership of Labour at the minute is that every day is somehow, impossibly, worse than the last.

This trope seemed to have run its course when John McDonnell, the Shadow Chancellor, ended the day of the Autumn Statement clarifying that of course he condemned the murder of tens of million by Mao Tse-tung, the Communist tyrant whom he’d quoted in Parliament earlier that day.

Yet it seems that assumption was a mistake. The upcoming vote on intervention in Syria seems to have put the Labour leadership under such pressure that it teeters on the brink of open civil war.

Corbyn has exhauasted the patience of many in the Shadow Cabinet by seeming to go behind their backs, via the media and his Momentum militia, to oppose air strikes on Syria which many of them support.

Indeed, Labour MP John Spellar has gone so far as to accuse his leader of trying to stage a ‘coup’ to take over the very party that he was overwhelmingly elected leader of not three months ago. Today’s papers are full of talk of resignations and rebellion.

The prospect of a free vote seems the option least likely to cause an immediate split – although many of Corbyn’s opponents think that failing to take an issue on a matter of war and peace would fatally undermine what credibility the party has.

However, a free vote with the Shadow Cabinet sending pro-Government signals would likely lead to an overwhelming defeat for Corbyn’s position. Thus he may attempt a whipped vote, regardless of the consequences.

It shouldn’t have come as a surprise that Corbyn is doing so badly. When he was elected there was much talk of a short-term boost, or of it taking a while for the truth about Labour’s new leader to penetrate the public consciousness.

Given how terrible Labour has proven at getting rid of deadweight leaders, it was also assumed that it would take some time for the Parliamentary Labour Party (PLP) to get bold or desperate enough to move against him.

Such assumptions have been revealed, it seems, simply as attempts to impose the normal patterns of British politics on a completely different set of circumstances.

Corbyn, McDonnell et al are not like Michael Foot. They have no Government experience, and take pride in it. They have never been confined to a Government line in their voting, let alone defended one from the front benches as Foot did.

They are clearly unwilling to moderate their views now they’re in office – and whilst that drives Labour MPs mad, they do retain the support of a majority of the Labour membership who, it should be remembered, very much did not vote Corbyn in as a spokesman for the views of the PLP.

Corbyn and McDonnell also have no interest in reigning in their supporters: if their time in office is limited, they need to do as much as possible to strengthen the position of their sympathisers in the Labour machine.

It’s been argued that Labour MPs can take their time in undermining Corbyn due to the security offered by the Fixed Term Parliaments Act (just one more reason to reintroduce flexible Parliaments).

However, it’s now almost impossible to see Labour reaching 2020 – or even May’s elections, the much discussed decision point – without either deposing a leader or suffering a string of damaging Shadow Cabinet resignations.