Rupert Cornwell: She's in, but Democrats can't help worrying she won't win

She's in, but can she win? That is the question after Hillary Clinton's announcement yesterday that she is seeking the Democratic presidential nomination in 2008. The timing was a tactical surprise, but the substance of it had been expected for months. Technically, she is merely forming an exploratory committee, but there is no more doubt she is running than that Barack Obama, the Illinois Senator who is her biggest rival, will make it official in a speech at Abraham Lincoln's house in Springfield, Illinois on 10 February.

Name recognition, money and a proven ability to raise lots more of it make her the clear front-runner on the Democratic side. In her six years as junior Senator for New York, she has moved carefully to shed her liberal image, taking centrist positions on many issues and launching bipartisan initiatives with Republican colleagues. By common consent, she has been an excellent Senator - even though she made the mistake of voting for the Iraq invasion in October 2002. To the dismay of the left, she has never recanted that vote, blaming the present mess not on the strategy, but on the execution of the strategy.

But Iraq is not the only reason that many Democrats have a nagging suspicion that for all her fame, her proven ability and command of the issues, she cannot win. She remains a divisive figure, and polls suggest that more than 40 per cent of Americans will not vote for her under any circumstances.

It is not that she would be the first woman elected president - the same polls show that Americans have little against that novelty. There is something about her, people say: an excessively calculated way of doing things that has you wondering about her true convictions. Why, for instance, did she last year back the ridiculous proposal to ban flag-burning by law - if not to pander to the centre and the right? There is also the Bill factor. Hillary is not only the first woman with a good chance of winning the White House, she is also the first ex-First Lady with the real prospect of sitting behind the desk in the Oval Office. "Vote for me and you get two for the price of one," Bill Clinton liked to say as he campaigned for the White House in 1992 - when Hillary was already well known, not only as a brilliant lawyer but as a first Lady of Arkansas whose influence on her husband was huge.

This time, as the saying goes, the vices are versa. What kind of influence would Bill wield in a Hillary White House. She knows the ropes of the presidency, but then again, so does he, even more profoundly. As an inspirational speaker, he overshadows her, as he eclipses every other American politician of his generation (with the possible exception of Barack Obama). His popularity, if anything, has grown since he left office.

But then there is the bad Bill. Imagine, for instance, gossip page stories about him straying from the marital bed. Not only would they interfere with her campaign; they would bring back less pleasant memories of the Clinton era: Monica - "It depends what the meaning of 'is' is" - and the visible strains in their marriage as the scandal unfolded.

A Hillary victory and a two-term presidency would also mean that Bushes and Clintons had ruled the US for 28 straight years; do Americans want that kind of dynastic politics, verging on monarchy? But they might well get them - which is why Hillary's announcement only underscores why 2008 is shaping up as the most fascinating presidential year since, yes, 1992, when the first Clinton defeated the first Bush.