Is David Cameron a finisher or a starter? The question comes up because the pattern of his biography to date is that of a man who performs brilliantly under pressure and at the last minute. Academically, he was a late developer. At the age of 11 he was 13th out of 13 in his class at Heatherdown, his prep school, according to the mark sheet recently obtained by the Daily Mirror.
It was not until his last two years at Eton that he suddenly hit his stride. "An awakening interest in politics, a steely ambition and an academic facility flowered in him, seemingly simultaneously," say his biographers, Francis Elliott and James Hanning. "Not for the last time in his life, he suddenly burst from the pack when the prize was in view." He went on to take a first at Oxford. He thus embodies, incidentally, the argument against selection at the age of 11 – weaning his party off its attachment to grammar schools being one of his genuine modernising achievements.
He came to the leadership of his party suddenly. Something of a myth has developed about his speech to the Tory conference in Blackpool in October 2005: that he seized the crown from the favourite by delivering one good speech without notes. In fact it was only a moment – albeit the most important one – in a few months' campaign in which Cameron used the shadow education portfolio to show that he was the party's best anti-Labour weapon.
At the moment of maximum danger since he became leader, when Gordon Brown thought of calling an election in the autumn of 2007, Cameron did it again. A good speech, but more importantly a clever proposal to cut inheritance tax, spooked the Prime Minister and forced him to call it off, costing Labour a fortune and Brown much of his reputation.
Thus the conventional wisdom was that, when Brown could finally put off the election no longer, Cameron would rise to the challenge and carry off the prize once more. So are the doubts that convulse his party now like the final setback inserted by the celestial playwright to enhance the emotional power of his eventual triumph?
Or does the conventional wisdom have Cameron the wrong way round? Because there is an alternative reading of the Tory leader's story that says he is a starter; brilliant at first impressions but lacking follow-through. That he did not need much more than a plausible front and a couple of good lines to win the leadership of his party in a thin and compromised field. That Brown messed up the early election all by himself by delaying until after the conference season. And that the opinion polls have tightened because Cameron hasn't done his policy homework.
It's an interpretation of Cameron that was reinforced by his reply to the Budget speech last week. He started well. He welcomed the Chancellor's lifting the stamp duty threshold to £250,000, which the Conservatives have advocated for three years, and he had some good lines about Cabinet ministers "looking at their BlackBerrys" because they couldn't think of a single reason why the country would want another five years of Brown.
He also mocked Liam Byrne, the Chief Secretary to the Treasury, whose memo setting out the precise duties of his civil servants was leaked a while ago: "Get him an espresso or there'll be trouble." Oddly, Cameron's staff edited that line from the Commons official record, possibly because it was a personal attack, but left in his description of Byrne as "Baldemort", which is more personal.
But Cameron quickly ran out of steam on Budget day and ended up declaring rather limply: "We need a Conservative Government to clean up the mess made by this Labour Government and to stop another five years of debt, waste and taxes."
In those three words, Cameron managed to sum up his party's dilemma.
Debt: for most voters, government borrowing is not real. It is not like bin bags in the streets or bodies unburied. When Cameron says, "We can't go on like this," the honest response is mostly, "Why not?" People tell pollsters that it is time for a change, but when it comes to doing something about public debt, cutting services or public sector jobs, that is not the change they mean.
What about waste, then? Tories may care about it more, but all governments waste money, and Tory waste-busting is essentially the same as "cuts".
Finally, taxes: that is where something strange has happened. A YouGov poll two weeks ago found that voters think that the Conservatives are more likely than Labour to put up taxes (by 37 per cent to 26 per cent). This is where the Tory strategy has gone wrong, reversing the historic reputations of the two main parties on tax. People have received and understood the message that the Tories are serious about cutting the deficit, but they don't really believe that the deficit is a threat to their well-being. So people think Cameron would put up taxes, which they do care about, to fix a problem that they don't care about.
That means that Cameron is reduced to playing defensive politics. Last week he was forced to make a "personal promise" to pensioners, to protect the winter fuel payment, free bus passes and TV licences, and the pension credit. Labour leaflets around the country suggesting that the Tories would cut them were outrageous, but effective, because they fit a story that is not going Cameron's way.
Now, we will find out what the Tory leader is made of. He has his back not to the wall but to the edge of the precipice. The Budget has set the terms of the election. In past elections, little has happened to the opinion polls during the campaign. But this time, the smallest movement could decide the outcome.
I suspect that Cameron really is more of a finisher. He'll need to be.
John Rentoul's blog is at www.independent.co.uk/jrentoul