Comment: Profile - The three faces of the First Lady : Hillary Clinton

As she enters the race for the US Senate, some say she has had plastic surgery - but perhaps it is naked ambition that is making her glow. By David Usborne

Hillary Rodham Clinton, we have been unreliably told, sneaked into the surgery of a Manhattan plastic surgeon sometime this summer for a bit of nip and tuck. She has denied it, of course, but why wouldn't she have done? She would hardly be the first fiftysomething to seek some help with his or her lines.

The tabloid reports were persuasive for another reason, however. The alleged make-over was the perfect metaphor for the much more profound transformation that Mrs Clinton was about to undergo. What we had been expecting for months, Mrs Clinton finally confirmed before the cameras on Tuesday: she will try to become the first wife of a serving American president ever to be elected into political office.

History-making aside, this is not a small step. Instead of spending the next year in the comfort of the White House playing at First Lady, she is plunging into political rapids that have no equal for their ferocity. The race is for a US Senate seat in New York, a state famous for its unforgiving battering of candidates, and her opponent will almost certainly be the take-no-prisoners Mayor of New York, Rudolph Giuliani.

In very short order, Mrs Clinton must make some big changes, almost all to do with getting away from her husband. To establish at least some tenuous bona fides as a New York resident, she must quickly pack her things and move to the pounds 1.2m home recently purchased in leafy Chappaqua, in Westchester County, east of New York City. But she must also distance herself from the President and the White House politically. Voters want to see her as candidate Hillary, not as First Lady Hillary.

Why is she doing this to herself? Won't eight years beside the world's most powerful leader be enough? Aren't there heaps of jobs she could take as the wife of a former president that would give her scope to influence our world - lecturer, ambassador, special representative, writer, whatever? At the very least, why didn't she wait two more years when she would have the chance to run for a Senate seat in Illinois, the state she was born in and where the game of politics is a little less violent?

To find any kind of answer - beyond the crude ones such as ego and unbridled ambition - we might trace the progress Mrs Clinton has made since she left home in suburban Chicago in the early Sixties. She has never behaved like a person willing to stay in the shadows of anyone, even a president of the United States. To her followers, Mrs Clinton long ago became an icon of a new post-feminist America. This race is only the next step. And if she wins, she could go forward to run for the presidency in 2004. She has it within her grasp to break the highest glass ceiling of them all - to become the first woman to run the White House.

So we should not be surprised at what she is doing. Her oldest friends will remind you of the day in the ferment-filled year of 1969, when she took the podium as student speaker at Wellesley College's graduation ceremony. A US senator, Edward Brooke, had just implored the students to turn their back on social protests and show some adult responsibility. The then Hillary Rodham discarded her prepared remarks and challenged the senator head-on, saying hers was a generation that meant to change the world.

Hillary later married Bill Clinton from Arkansas, whose own political ambitions were worn on his sleeve and every other part of his person. As he climbed the greasy pole of public office in Little Rock, she pursued a career of her own as a partner in the Rose law firm. By the time the pair reached the national stage in the presidential campaign of 1992, all of America could see the governor's wife was no stay-at-home. She famously mocked the "Stand by your Man" ethic as sung by Tammy Wynette. When quizzed one day about her work at the law firm, she famously replied that she was not one to stay in and bake cookies. One campaign button that year offered this about the Clintons: "Buy one, get one free".

Thus began the start of an extraordinary and painfully twisting relationship between Mrs Clinton and the rest of America. For some in the country, she was already beyond the pale. The conservative cottage industry that demonises Hillary was quick to begin grinding. But the new First Lady, who was enjoying high approval ratings at the time of her husband's inauguration - about 67 per cent - pressed on. She quickly agreed to head a presidential commission on overhauling the US health-care system. Symbolically, she eschewed the traditional East Wing quarters of a First Lady and moved into the executive territory of the West Wing.

Very quickly those high poll numbers nose-dived, hitting 46 per cent by the start of the 1996 re-election campaign. Mrs Clinton's universal health-care project famously imploded. America reeked with schadenfreude. You can debate whether the sudden upwelling of animosity towards her was caused by the healthcare debacle or whether the animosity was already there from day one of the new administration, and thus she never had a chance, in political terms, to succeed. It has often been posited that Mrs Clinton inspires hatred precisely because she is a woman who pushes. "There was no question that many people wished Hillary Rodham Clinton to fail," Erica Jong wrote in her book What do Women Want?. "She represented the new woman of the 21st century, the woman our daughters are practising to become."

The second Clinton term might have been characterised, in part, by the newly demure role assigned to the First Lady. She did not bake cookies, but she performed less controversial duties such as attending the UN women's conference in Peking. This was partly on the orders of the campaign strategists and partly because of the by-then unrelenting scrutiny the First Lady found herself under for her roles in assorted Clinton scandals. She is the first wife of a president who has been obliged to appear before a grand jury. Three different grand juries raked over her past to do with everything from her oddly lucrative commodity dealings back in her Arkansas days, to Whitewater, Travelgate, the death of her alleged lover, the White House legal adviser Vincent Foster, to questions about billings by the Rose law firm. Mrs Clinton has never been charged with anything, but each episode helped to polarise opinion about her. But then Monica happened. And that is when analysing Hillary Rodham Clinton becomes really interesting.

As the Lewinsky allegations first surfaced, Mrs Clinton's instinct was to lash out - at the "right-wing conspiracy", as she put it, that was afoot to ruin her husband. But in the ensuing months, as the evidence of hanky-panky in the Oval Office mounted, she adopted precisely the kind of role she had forbidden herself before. She absolutely stood by her man. And the American public was impressed. By the end of last year, when Bill Clinton was impeached for his sins and still his wife maintained what many perceived as a courageous and dignified silence, her approval rating had rocketed to more than 80 per cent.

It was exactly in the same period that Hillary began seriously to think about running for the seat which was to be left open by the retiring Democratic senator from New York, Daniel Patrick Moynihan. Exactly what drove her to say yes to the challenge only she can fully know. Perhaps, after submitting silently to so much humiliation, month after month, she concluded that she was due some fun of her own. Was she being driven by a sense of frustration with a husband who had so royally mucked up his second term all because he couldn't resist the flash of a thong panty? Somehow, maybe this is his punishment. Whatever else, she must have been encouraged by the sudden and enormous welling of public sympathy towards her. And therein lies a marvellous irony. She agreed to carry the standard of post-feminism into battle in New York because of poll numbers inflated by her most old- fashioned loyalty to a philandering husband.

Already, those numbers are looking less rosy. A new CNN/USA Today poll shows Americans split on whether Mrs Clinton should be running at all. In New York state, according to a New York Post survey, a majority wishes she would stay away. Polls matching Hillary against Rudy, put the Mayor ahead of her by up to 11 points. She has not been helped by missteps already made, most notably during a meeting with the wife of Yasser Arafat two weeks ago, when Arafat accused Israel of unleashing poison gas against Palestinians and Mrs Clinton enraged New York Jews by saying nothing to contradict her.

This will be a vicious race. There is a deep pool of people who will never be able to stomach Mrs Clinton in New York, as there is everywhere in America. If it shrank a little during the Monica months, that drought is over. On Tuesday she insisted that the contest will not be about her and Giuliani but about the issues that matter to New Yorkers. Well, there was one stretch of the truth right there. It will be entirely about the personalities of the candidates. About her "left-wing" tendencies and his strangely diminished capacity for compassion. About her scrapes with the grand juries and his police-state dictatorship.

But this much we know for sure about Hillary Rodham Clinton: she does not shy away from a fight. She relishes a scrap. And if her features look suddenly youthful again, probably it has nothing to do with collagen. What is rejuvenating her is the prospect of the 12 months ahead.