Hubris, the ineradicable flaw that helps humans to clutch defeat from the jaws of victory, has played merry havoc with this eventful US presidential primary season.

For most of last year it masqueraded as a sagacious self-confidence that animated Hillary Clinton's presidential ambitions. She had the name, her people said, she had the money, she had the experience, the connections, the command of policy. What could possibly go wrong? This certainty, of course, was more than just the usual product of an insufficiency of humility. It was the central, self-reinforcing argument for the Clinton candidacy. The more they could persuade people that she was invincible, the more invincible she would in fact be.

Nemesis showed up, or so it seemed at the time, in the snows of Iowa. When she came third in the caucuses there, her invincibility melted away, and with it her campaign's self-confidence. But, though we didn't know it at the time, hubris had not disappeared. It had merely switched sides.

In the frantic days between Iowa and New Hampshire, it was now Barack Obama's people who were walking with destiny. As his opinion poll lead widened, plans were laid for a victory rollout of big endorsements in the days after New Hampshire. There was talk of a quick kill. Mrs Clinton's victory there put a stop to all that and made everybody swear never again to fall for the temptations of premature celebration.

But, human nature being what it is, that resolution has lasted barely a month. Since last week's Super Tuesday, the Obama campaign has given up trying to suppress its confidence. With another sweep on Tuesday in Virginia, Maryland and the District of Columbia, Mr Obama extended his current winning streak to eight primaries. His victory speech that night virtually ignored the Democratic contest still going on and focused instead on the general election campaign he now expects to be fighting against John McCain, the presumptive Republican nominee.

Then on Wednesday, David Plouffe, Mr Obama's campaign manager, told reporters it was now “next to impossible” for Mrs Clinton to finish the primary campaign with more elected delegates to the party's nominating convention than Mr Obama, proof of his campaign's burgeoning self-confidence.

There are two categories of Democratic delegates. Four fifths of them are directly elected in the long-running series of primaries and caucuses now under way, in approximate proportion to the votes cast for each candidate. But a fifth are ex-officio “superdelegates”: senior party panjandrums who can vote as they wish. Mrs Clinton is generally thought likely to win a majority of these, but there is a growing sense that, if Mr Obama emerges ahead in the popular vote - and therefore in the elected delegate count - the superdelegates will be morally and politically obliged to side with him. The message, therefore, implicit in Mr Plouffe's observation is: it's over, we've won.

That may not amount to hubris, but with more than a third of all the elected delegates - more than 1,000 - still to be chosen in the remaining states to vote, and with Mr Obama clinging to a current lead among that category of delegate of a little more than 100, it could certainly count as premature.

Even if Mrs Clinton cannot notch up margins large enough in the forthcoming states to overtake Mr Obama, with a string of victories she could mount an alternative argument. She is now pinning all her hopes on the next big states to vote - Texas and Ohio - on March 4, where polls suggest she has a strong lead. They are the kind of states that are host to a larger concentration of her types of voters: blue collar, less affluent, old and Latino.

If she wins them and goes on to carry Pennsylvania on April 22, she can claim not only to have renewed momentum, she will have pulled off a remarkable feat. Mrs Clinton will have won in seven of the eight biggest states - accounting between them for 43 per cent of the US population. There will be a struggle over two of those states - Florida and Michigan - because they are banned from sending delegates to the convention since they broke Democratic party rules by voting early. But that still adds up to an impressive collection of big states.

Is this feasible? Can Mrs Clinton now turn the newly popular conventional wisdom on its head once more and pull out a win?

The answer is yes, but only, I think, if she can somehow transform her message in the next two weeks. The truth is that until now she has run a campaign that will become a model of how not to win elections.

It began a year ago with the insistence on her invincibility, as though she did not need to earn the nomination but was owed it by a grateful party.

It continued with her emphasis on her experience and familiarity with the ways of Washington in a year in which it was clear to all that voters wanted change.

Then when she ran into trouble after the first few contests, she made the catastrophic mistake of letting her husband run riot for a few crucial days and remind voters of all that they feared about a Clinton restoration.

Her one remaining asset after all this is that her core voters are still the Democratic party's base: working-class types struggling to make ends meet in a weakening economy.

But even they may be starting to waver in the direction of Mr Obama's inspiring rhetoric. She has two weeks to persuade them that she has a real plan to help them.

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