If the first, instant cliché was that "Dave needed a game-changer and didn't get it", the second ought to have been "Is Clegg what the hype said Cameron was?"

When all the endless puff pieces wrote up David Cameron's coming victory, the man that anticipatory narrative required was the man Nick Clegg was being last night. As the press slimed him, his temper didn't slip, as the biggest opportunity of his life came his way he didn't freeze in the headlights and, when it came to saying nothing competently and plausibly, he's still the man to beat.

What the debates are proving beyond doubt is that there has been an unadmitted consensus in British politics. And that's what has been central to Clegg's success, for only in The Election with No Issues could the Lib Dem leader prosper. That Cameron has not been able to delineate dividing lines sums up his failure in making this his "change election". Surrendering that claim of right to the emptiness of Clegg has been worse than a mistake, it's been embarrassing.

Some Conservatives are already grumbling that the lack of reasons to positively vote Tory is down to nebulous campaigning slogans such as "the big society". "Waffle," as one frontbencher put it to me, "and badly written as well." But that's to mistake symptom for cause: the precise reason why Cameron, instead of running on biting Blairite pledge cards, is trying to float into Downing Street on fluffy Letwinian clouds is because he has deliberately eschewed stark differences.

His strategy since the start has been summed up by self-conscious efforts at "decontamination", hence an acceptance of the critique of the left about the party and, worse still, total and absolute submission to their fundamental framing of the terms of British political debate. Hence Cameron's disastrous decision to stick to Labour spending plans, robbing us of any honest ability to denounce Brown's historic failure over the economy. That he then opted to stick, at all costs, to the discredited figure of Osborne as shadow chancellor merely made a bad situation much, much worse. That he promoted Osborne to also actually run the general election campaign as well is playing out just the way it was always going to.

Take Osborne spinning. When, in the throng after the debate, he screeched that last night was a triumph for Dave, and that Cameron cleaned the floor with the rest of them, and all the other silly, exaggerated stuff, sure, it's reliably off-putting for the punters, but it's infinitely worse with the people Osborne believes he impresses, other politico-media types. And this is the thing that runs most contrary to the lazy predictions about the election: whatever else we all thought about Team Dave, we thought they'd be able to spin. As it is, from the leader downwards they're failing in the area where even those of least well-disposed towards them thought they would do a good job.

Take Cameron – I always assumed that on his feet, in the debates, he would continue to do a good, Reagan-esque job. Whatever the actual character of the man, I assumed his telly persona would remain a sunny disposition, interlaced with thinking-on-his feet zingers. Instead, and from Brown in particular (even, last night, including boasts about pensions!) open goal after open goal was put in front of Cameron, and it wasn't even that he missed – he didn't even shoot. What we got from Cameron, in cutaway shot after cutaway shot, was gurning, here an arched eyebrow, there a shake of the head, and always that idiotic prefect's "disappointed pout". Compare this with Clegg's centre-stage self-assurance: it's a ridiculous thing to have to boil democratic debate down to, but then as many of us have said, it was a ridiculous decision for Cameron to push for these debates. Without them, I have no doubt that he would have won a working majority – with them, he has needlessly thrown away the election.

What's even more depressing is the retreat already, even before we've blown it, into self-delusion of too many camp-followers on the Tory side. The most absurd instance is the fantasy that we will be saved from Cameron's incompetence by surpassing Liberal incompetence. That they won't, in a hung parliament, go into a "progressive majority" with Brown and Mandelson and Miliband all variously aching to give it to them.

Then there's the ludicrous notion that Clegg has "peaked" or that he is losing some vital momentum: the man has broken through. I would say, single-handedly, but the whole point is that Cameron needlessly gave him the vital helping hand he needed. Tory-paid propagandists, and more forgivably, honest tribalists, may well put their fingers in their ears and whistle a comforting tune, but if the leadership now does the same, they are doing the party one last, fatal disservice.

Every Cameron assumption up to this point has been wrong. Not least their manic presumption that Brown would implode in the debates and more generally: he hasn't and won't. All that's left to us now is Cameron's temperament. This is a man who has spent four years being written up as the next prime minister and is now spending four weeks tossing the keys to No 10 away: that's pressure he hasn't faced before, and the retreat from the stage thus far doesn't suggest good news.

It's no wonder William Hague's looking and sounding so depressed. It's one thing going back to a job you came to hate, however profound your sense of duty – it's going to be quite another inheriting a party in the state Cameron will have left it in.

• More Guardian election comment from Cif at the polls