The conventional wisdom is that Cameron had to win last night's debate. It's wrong.

Momentum's indispensable to winning elections.  If you can gain it and keep it, you'll probably win, all else being equal.  If you gain it and lose it, you probably won't.  Nick Clegg shoved his way into the spotlight last week, and his poll ratings soared. But they seemed to peak during the last few days - as media smiles turned to snarls (with more to come this weekend, doubtless).  So his strategic aim yesterday evening was to keep the momentum he gained.

It's far from clear that he did, and my best guess is that he didn't.  The sum of the post-debate polls and this morning's headlines suggest a Clegg/Cameron draw - not the champagne-bath romp the former enjoyed first time out.  And there's still two weeks to go until polling day, after five years of helter-skelter polling that's seen Labour eleven points ahead in the late summer of 2007, and the Conservatives 24 points ahead the following spring, with the final leader's debate next week focusing on the economy.

So the the conventional wisdom that Cameron had to win overwhelmingly yesterday is no more or less true than the view that he had to win in such a way last week...or next week.  For what it's worth, I believe that he doesn't have to win any of them overwhelmingly.  As I've written before here, what he has to do is get the voters to focus on themselves, not the politicians - on salvaging the economy as well as delivering change. I'm not convinced that we can out-trump the LibDems on the latter.

Reminding voters of the further damage Brown would wreak on their wallets, budgets, mortgages and jobs is a bit like lighting a gunpowder trail.  There's no knowing whether the flame will reach the barrel as intended. Obviously, the debates play a part in keeping the fuse going - particularly next week's on the economy - but so did Ken Clarke's warnings at the Party's press conference on Tuesday, or his FT piece in the same vein a day later.  If anyone had to do anything last night, Clegg had to keep the momentum.

But - as you see - I suspect that the importance of the debates has been over-egged, unless one of the three leaders crashes and burns.  This hasn't happened yet.  It almost certainly won't next week.

Paul Goodman