If the bookies are right, Jeremy Corbyn is the political equivalent of a nice slice of wholemeal, browning fast. He’s toast. Smart money, supposedly superior to any opinion poll, says a Labour leader elected by a landslide will be gone within a year of his triumph.

The claim ought to be disturbing, even for his enemies. You might despise Mr Corbyn’s politics, but saying so – or acting on the opinion – won’t solve a fundamental problem. The rift between Labour’s membership and its parliamentary representatives is deep. It might even be permanent. So where’s the victory in a leadership coup?

MPs can say, justifiably, that they act for all of their constituents, not just activists. Parliamentarians can claim, equally, to be bound by conscience, and therefore entitled to defy public opinion or the party whip if there is a pressing need. Mr Corbyn’s impressive record as an inveterate rebel is not, in that regard, his best weapon.

But MPs get to Westminster thanks to, and on behalf of, a party. Its members do most of the work and pay many of the bills. In essence, they have legal ownership of the institution. If some bright, ambitious sort with a PPE fancies giving politics a go as an independent candidate, he or she is welcome to try. Those who regard themselves as Labour-inclined know better.

In September, Mr Corbyn trounced Andy Burnham, Yvette Cooper and Liz Kendall. He took 59.5 per cent of votes cast. Forget the three-quid arrivistes, the mischief-makers and the political tourists: the winner gained the support of 49.59 per cent of party members. They gave him 121,751 votes against Mr Burnham’s 55,698. And they knew precisely where Mr Corbyn stood on Britain’s interventionist wars.

Most Labour parliamentarians and the usual superannuated bag-carriers were not too pleased by September’s outcome. With surpassing gall, some maintained that “their” party had been taken from them. When that piece of illogic collapsed, they took to saying that 49.59 per cent of the people without whom there is no party had been duped, or gone mad. The old guard were shouting into the gale.

A truth remained. An ancient issue, common to all parties but acute in Labour, had been exposed: MPs and the membership were utterly at odds. Mr Corbyn’s politics and style were deemed “electorally disastrous” by the former – a group that had just endured real electoral disaster – but welcomed, indeed lauded, by the latter. Now, in November, something has to give.

It is an authentic pity that Labour, on both sides, has wound up treating a solemn decision over Syrian air-strikes as an excuse to re-run a leadership contest. Few voters are liable to be impressed. David Cameron’s serious attempt to make a case for bombing requires a serious response. Shouting “Corbyn must go”, or “Party democracy must prevail”, is hardly rising to the occasion.

The Prime Minister wants to win a Commons vote on the issue of war. With dissidents on his own side, and with the Scottish National Party concluding that his case is dangerously weak, he needs Labour support. At Westminster, that party is a paradox: one leader and precious few who are willing to be led. Meanwhile, the membership stand by their man.

After a series of unfortunate events – as Mao didn’t say – Mr Corbyn has to work out how he can still speak “for Labour”. But his party enemies also have to decide what they are about. Is this an argument over the Prime Minister’s rationale, over the rights of conscience, or just the first and best chance to airbrush the accidental leader from the public memory?

Several Labour figures such as Hilary Benn, the shadow Foreign Secretary, have quibbled over Mr Cameron’s prospectus for war. They have claimed to be waiting for the precise wording of any motion on which they can vote. This is waffle. The choice is to vote for the Prime Minister’s thin case – allies would appreciate a few British bombs, “our influence” would be enhanced – or stick with their party leader when he warns of dire consequences.

To the outsider, the eve of war doesn’t sound like a moment to be taking revenge on Mr Corbyn for the crime of winning a party election. He would meanwhile require some front (as they might say in Islington) to deny his enemies a free vote come the hour. He could also apologise for insulting his shadow Cabinet by writing a letter to MPs setting out his opinion while efforts to agree a strategy were still taking place. Nevertheless, his critics have some explaining to do.

If their only aim is to do in Mr Corbyn, they have no right to fancy titles and “seniority” within their party. This moment, with the drones and fighter-bombers prepared, is far too important for weary Left-Right Labour games. If Mr Cameron gets his way, right or wrong, people will die. Another bout of internecine arm-wrestling is, or should be, neither here nor there.

If Mr Benn and others like him take a more serious view, however, they should spell it out. “Doing something” about Islamic State does not count as an answer. Is Mr Cameron right or wrong? Since it’s clear that much of the shadow Cabinet – “ready to resign”, indeed – have already reached a decision, they must state their case. Hiding behind those useful “Labour split” headlines simply to rearrange the shadow Cabinet seating is worse than cowardly.

Those who elected Mr Corbyn are entitled to wonder what he has done to deserve all of this. You could say, fairly, that he and his coterie have done nothing right, whether on so-called “shoot-to-kill” policy, or on the best place to deposit Mao’s Little Red Book. Given council results in Fife, the rolling-back of the Scottish National Party remains, for one thing, a forlorn hope. Then again (and in so many ways) Mr Corbyn is no Jim Murphy. He hasn’t lost 40 seats.

The Oldham West and Royston by-election will no doubt tell a different story. Would the leader’s enemies relent in the event of an unlikely triumph? Of course not. That is why their behaviour in the debate over an expanded war effort in Syria is troubling. They are behaving as opportunists whose first loyalty, in all things, is to a status quo of party and state. Bombing, bloodshed, the national defence, matter just a bit more than that.

By no coincidence, the behaviour of his shadow Cabinet colleagues is exactly the sort of thing that got Mr Corbyn elected. The idea that he represents a “new politics” is laughable: he offers a retread of an ideological retread. But those in the PLP who resent their own party members and would vote dutifully with a Tory government for morally-vacuous Made-in-Britain bombing are a scandal.

Labour is near to the end of the road. That old “broad church” is a congregation divided against itself. If the MPs prevail and Mr Corbyn’s election is over-turned – for that’s the game – what are 121,751 members supposed to think or say? Where could they next cast a vote? Not for the advocates of war who subverted their anti-war candidate.