Matthew Norman: In the interests of his party, Clegg must walk the plank

As the pea-souper that has enshrouded Westminster for 12 months finally begins to lift and the political landscape becomes visible, we find ourselves gazing with pity upon a candidate for the title of World's Unluckiest Man. For a century that honour belonged to the fella who was drowning at sea when he was rescued by a ship. The Titanic. Just time for a wash and shave, and straight back down he went. It has been an eerily similar story for the new WUM, Nick Clegg.

Cast adrift a year ago by the shock shrinkage of a parliamentary party expected to surge towards or into three figures, Mr Clegg was relieved to clamber aboard a Tory vessel listing dangerously itself, and naturally thrilled to be made First Mate. If he has made mistakes since in helping to right it at his own crew's expense, what he cannot be blamed for is cutting the Coalition deal in the first place. For reasons long familiar (parliamentary maths, impossibility of coupling with Gordon Brown, conflated fear of sovereign debt contagion, and justified terror of dooming his party with the charge of dilettantism if it stayed on the sidelines), he had absolutely no choice.

Revisionists will soon dispute this, arguing that Little Orange Riding Hood skipped girlishly into the trap without noticing that, beneath the bonnet, a lupine David Cameron had exceedingly sharp teeth and a chin drenched in drool. Cobblers. Mr Clegg could do nothing else, and played a dodgy hand with enormous skill and chutzpah.

Whether he fully understood that doing so must gravely damage his party for generations, only he can know. My hunch is that he did, because he is a very bright chap and you'd need to be a quarter-wit not to appreciate that a party of perpetual protest will suffer monstrously when it becomes the enabler of those its core support viscerally loathes; but that he convinced himself otherwise, like the denial stage terminal patient who believes that positive thinking will keep him going until the miracle cure arrives. There can be no miracle now for Mr Clegg. The prognosis was not delivered last week by AV and council voters. That was the confirmatory second opinion. His leadership entered the palliative stage months ago, when the public's vague suspicion that he is a shifty chancer – as implanted by his fibbing to Mr Cameron about Labour's AV referendum offer – metastasized into certainty over tuition fees. There he did saunter naively into bed with the wolf.

Once a leader's face and name elicit a universal, reflexive snort of contempt, there can be no recovery. Gordon Brown's clumsy danse macabre to the grave after clucking up the snap election taught that. It didn't matter an iota whether his subsequent disasters were due to rank incompetence, sheer misfortune or forces entirely beyond his control. He took the hit for each and every one because the public perception of him as a giant one-eyed chicken had been set in concrete. Now that the punters have clocked Mr Clegg for a power-hungry charlatan, however unjustly, nothing will change their minds. He can posture as saviour of the NHS all he likes, and it will do him not a scintilla of good.

Gordon delivered other helpful tutorials, of course. He also taught how, in the absence of a ready-made replacement and the presence of a parliamentary party paralysed by panic, the most desperately sick leadership can be kept alive until a general election. Mr Clegg's one stroke of good luck is that life in coalition has degraded the reputations of the three most obvious potential successors to him (Messrs Cable, Laws and Huhne) almost as much as his own.

But the most important Gordonian lesson of all is that euthanasia is always preferable, for those by the bedside and the wider family beyond, to an excruciating slow death. Had David Miliband jumped ship with James Purnell, or Alan Johnson struck even as late as the winter of 2010, Labour would surely be the largest party in parliament today, and more than likely in a progressive alliance with the Lib Dems. For the want of a little raw courage from Labour's living dead, a long period of Tory rule, if not hegemony, stretches ahead.

For now, Mr Clegg remains useful to a PM well aware that, second only to a sustained recessionary relapse, the greatest threat to winning an outright majority is a regressive rightward lurch. It is very much in his interests that Mr Clegg remains on board as ballast against the Leviathan of neanderthal right-wingery slowly unfurling its tentacles on the back benches.

It is absolutely in the interests of Liberal Democracy, however, that Mr Clegg goes overboard. Ideally he would accept the futility of his position and walk the plank. If not, he must be pushed. Whatever the flaws of his successor, is it imaginable that Labour would have failed to improve its position a year ago under anyone but Gordon?

As with Labour then, so now for the Lib Dems, it is primarily about damage limitation. Under Mr Clegg, be the election in four months or four years, they are heading irreversibly towards a cataclysm in which they would be lucky to retain a third of their seats. Under A N Other, they would have at least a chance of surviving as a relevant, if much diminished, parliamentary force. Mr Clegg's Icarus-style descent isn't fair. One of the good guys, he doesn't deserve the unthinking demonisation in which too many of us have lazily indulged. And that is the precise point. When all fair analysis of a politician's bona fides and abilities is replaced by auto-contempt, when he becomes the catch-all repository for every passing grievance, no amount of bravado about dusting himself off can disguise the fact that the game is up.

Now that the fog is clearing, we see the results of a party sleepwalking into the valley of death behind a lethally toxic leader, and Lib Dem MPs more clearly than anyone. Facing them on the Labour benches sit those whose shameful cowardice has saddled themselves with Opposition, and the country with a centre-right government growing stronger and more commanding by the day. It would be an act of suicide not to glance across the House and conclude that, while this may not yet be the moment to act, it is high time to start stockpiling the morphine.