Come on, Ken - can't you do better than this?

The whole saga, from the casual misuse of taxpayers' money in unscrutinised grants to the cavalier refusal to accept serious lapses or take responsibility, is a sign of what is rotten in Livingstone's London.

The Mayor should have asked his ally to step aside on grounds of self-preservation alone. In clinging on to him, he made an error that is typical of the late Ken period - refusing to do the right or even rational thing lest it give his enemies a scalp.

So he failed to suspend Mr Jasper when the allegations first surfaced in Andrew Gilligan's reports in the Evening Standard on the maladministration of funds to ethnic groups in London. When Mr Jasper's own aide stood down, having lied about a foreign trip, the Mayor merely suspended his adviser instead of taking the initiative and removing him. Now he refuses to accept that the race adviser has erred - while accepting his resignation to get him out of the way in the Mayoral election campaign.

Two months from the vote, Mr Livingstone is in more trouble than I would have expected. He is falling back on a "progressive" Left Labour rump of support, rather than emphasising his appeal as a figure who, for all his peculiarities, once evoked admiration across the political divide.

I think back to the first Mayoral campaign in London when Tony Blair's party machine was about to make its first mistake in imposing an under-par candidate in Frank Dobson. This highhandedness and Ken's fightback were enough to convince me that he deserved a chance - not because I liked his potty GLC record but because he was a genuine London populist and a figure who burned with enthusiasm for the job.

Unlike anyone else in the field, he knew exactly why he wanted to be Mayor and the voters felt the enthusiasm, too. Second time out, with a few more reservations along the way, Mr Livingstone still felt like the right figurehead for London. Even Blair indulged in a rare portion of humble pie, saying that he had been wrong to block the party renegade's way to the job in the first place.

This time, it is a far harder fight for Ken as any third-term incumbency inevitably is. And yet instead of reaching outwards, Ken feels more self-absorbed, inward looking and self-selecting. Watch the TV footage of him ranting as the London Assembly questioned him on Mr Jasper - "sanctimonious hypocrites every one of you - you haven't earned respect," was a ghastly moment.

The Assembly is not the sharpest scrutiny body on the public payroll - and how much would Ken like it if it were? But really: it is not his place to speak to it as if it had no right to exist. He sounds like ex-President Putin dismissing rival parties in Russia. Tone is all-important in politics because it often tells us as much about a candidate as carefully rehearsed policies do.

Look at Boris Johnson, struggling manfully to be serious - and ending up a bit boring and neutered as a result. He cannot quite unite his old self and what he is trying to be. Mr Livingstone's tone sounds to me even worse, though: downright contemptuous of anyone who is not an outright ally. He assumes he should have the job again - but exudes no joy in it, only a sense of entitlement - always a risky assumption.

A clever anti-Boris campaign would not merely whip up ancient Labour class hatreds as the party's spring conference did. It would point out that running London is a complex job, with a lot at stake in terms of money and reputation, and say: "Are you really going to entrust one of the greatest cities on earth to this charming but unreliable chancer?"

Perhaps that is where Ken will go next. It is certainly where the big Labour guns are beginning to train their fire.

But it assumes that their man can present himself credibly as the more conscientious and reliable candidate. The climate of denial surrounding the Jasper affair has badly undermined that claim.

The important people in this election aren't the London Tories who thirst in the desert for "one of us" in a top job and cling to BJ as a John the Baptist presaging the national gospel of David Cameron.

Nor are they the self-appointed guardians of the "progressive" tradition, like the signatories of the comically worded Compass letter, who think that only they can decide what counts as the politics of social progress.

Most London electors view both these self-righteous tribes as bizarre. They will assess their quality of life, the plausibility of the candidates, how far they trust them to make their own lives in the capital more enjoyable - and how comfortable they feel with the contenders representing them in times of acute stress or danger.

So where is Ken's effort to co-opt critical or wavering opinion? So far his campaign has run purely on the rights of incumbency and tribal loyalty. Lynton Crosby, the Australian strategist who is finally bringing some rigour to the Johnson campaign, must delight in this lassitude. He once told me (as the man who advised both an ageing John Howard in Australia and a wilting Michael Howard here) that the most powerful attack on a long-stay politician was "he used to be really good/sharp/tough but he's lost it now".

Unless he can energetically prove otherwise, the judgment may well form that Ken used to be fun and irreverent - but is now a political sclerotic whose time is up.

Really shrewd politicians don't fall for their own propaganda, however convincingly they deliver it. Blair believed simultaneously that he was the only man to run the country, and that he was always about to lose out to an unheralded Tory revival. Because Ken is so dismissive of the prospect of defeat, he increases the chances of it happening.

The shadow of the Jasper affair falls so long on him because it is emblematic of so many other weaknesses. Having sought to deflect the revelations of malpractice as a "lynching" and a "racist campaign", he still refuses to accept their fundamental truth.

I don't kid myself that the Mayor will 'fess up to errors of oversight or judgment. So he has to find other ways to show that he still deserves what was never intended when the Mayoralty began - a third term at the helm.

For the first time since he outwitted the Labour Party machine all those years ago, the awkward, compelling, flawed survivor in City Hall has a real fight on his hands. Can't you do better than this Ken?