There is rage coursing through the veins of today’s Labour party. Even before the latest act of self-laceration over Syria, it’s been bursting out from all but the truest of true believers in the new leader: rage, despair and bewilderment at whatever new low has been plumbed.

One minute it’s the shadow chancellor smiling as he quotes Chairman Mao in the Commons; the next it’s Jeremy Corbyn having to clarify that, yes, if a homicidal terrorist were massacring people on a British street, pausing only to reload, it might be OK to stop him with a bullet.

Most of this fury comes from the obvious quarters: the MPs, the former advisers, the longtime activists – the people who have devoted their working lives to the Labour party – boiling with anger at the serial unforced errors of their new rulers. The Corbyn camp will dismiss them, of course, as “Blairites” or “red Tories”. They’ll say their critics are whining because their brand of austerity-lite, soft capitalism has been jettisoned, dumped by men of principle determined to fight for economic justice and a more peaceful world.

That response could not be more wrong. It fails to realise that what enrages Corbyn’s critics most is not a doctrinal difference with the leader, but their assessment of the damage he is doing to the party. Their chief concern is over Labour’s prospects of ever again winning the trust of the British people and forming a government. And they want a Labour government very badly. In other words, they despair of Corbyn not because they are on the right, as the leader’s chorus would have you believe, but because they remain on the left.

Take this week’s autumn statement by George Osborne. There was so much to criticise, so much to oppose. You could have begun with the trail of broken promises left by this chancellor, who swore he would eradicate the deficit by May 2015 and who did nothing of the sort; who solemnly vowed to be bound by a new “welfare cap” only to break it on Wednesday; who tightened the belt on the poorest in July only to reveal four months later that the public finances had been magically transformed by the sudden discovery of a hidden stash of £27bn. What possible credibility does this repeat promise-breaker have?

The opposition could then have moved to the choices Osborne makes. His instinct in July was to punish the hardest-working and the lowest-paid, by slashing their tax credits. He only ran scared when he realised his ambition to reach No 10 was in jeopardy, spooked by rebellions on his own benches, in the Lords and on the front page of the Sun.

Unrepentant, though, he continues to slash the money available to local councils, bleeding them dry. With a 56% cut, he is depriving them of the cash they need to clear the rubbish, maintain the parks and look after the vulnerable. Try as they might, and the best councils have been stretching every sinew, town halls will simply not be able to provide for the frail and the lonely, the adults who need social care, or the young people with learning difficulties who need a ride to school. Those services, along with the local library or swimming pool, will be starved of money until they are gone.

All of this needs to be opposed, just as Osborne’s autumn statement needed to be forensically dismantled line by line. This was why Labour people were furious at John McDonnell’s flourishing of Mao’s Little Red Book. It was for the same reason Osborne and David Cameron were so delighted by the stunt, the Tory benches lighting up with red faces guffawing in unison. Both sides knew that Labour’s critique would be forgotten, buried by the story of a shadow chancellor already lampooned as an unreconstructed communist appearing to vindicate his accusers in the most ostentatious fashion imaginable.

It’s not just the ineptitude that infuriates the Labour leadership’s internal critics. It’s the sure knowledge that Corbyn and his lieutenants are allowing the Tories to get away with it. Allowing them to escape scrutiny on a day when they should be under pressure, so that Labour’s economics spokesman spends his few precious minutes of airtime not lambasting the cuts that will disfigure the landscape of this country, but debating the record of China’s murderous dictator. All because of the vanity that thought it more important to make a juvenile joke than to speak for the people who are, and who will be, hit hardest by a Tory government unbound.

But the gift this gives the Tories is bigger than just one day of easy, unopposed headlines. McDonnell’s bow to Mao, like his past praise for the IRA, or Corbyn’s reluctance to stop terrorist murderers or his refusal to sing the national anthem, or Ken Livingstone’s blaming of Blair rather than the killers for 7/7 – all these estrange Labour from large swaths of the British public, including that section of it that once saw Labour as its natural champion.

Canvassers on the doorstep ahead of next week’s Oldham byelection report incredulity among past Labour voters at the antics of the men at the top. As for the voters of middle England, some of whom at least will have to find Labour acceptable if the party is ever to return to government, the current leadership is all but urging them to stay away.

So when MPs or other Labour voices condemn Corbyn and his team, their chief motive is not ideological disagreement. It is their hardening conviction that, with each daily misstep, the ruling circle is making Labour unelectable and turning the Tories’ lease on Downing Street into a freehold.

That’s what they speak about privately. That’s what gets the veins bulging in their neck. Their belief that Labour is guaranteeing the Tories at least 10 more years in office: after which the NHS, the welfare state, the BBC, the country itself, will be unrecognisable.

What will it take to bring about a change? Perhaps the new ruling group itself will shift, realising that it will simply have to compromise with the electorate and start, say, blaming terrorists for terrorism. Maybe the young and idealistic who rallied in such impressive numbers to the Corbyn flag will wince once too often at the dinosaur attitudes of the men they have elevated, whether it be Livingstone’s casual insulting of the mentally ill or the much noticed allocation of the most senior positions to men rather than women. Or maybe they will simply turn away from a top brass that still carries the baggage of ancient left struggles, like those over Mao or Irish republicanism.

Or maybe it will fall to the trade unions to save the party they helped found. Note Unite leader Len McCluskey’s warning to Corbyn this week that the latter could no longer “say the first thing that comes into his head”.

Either way, something has to move. There is less time than some in Labour might like to think. The party’s reputation is declining with each passing day. Labour needs to rescue itself, not for its own sake – but for the sake of the country it once aspired to govern.