First Lady in waiting steps centre stage to boost her husband

The list included Howard Dean, once Mr Kerry's fiercest rival for the nomination and the man who electrified audiences on the campaign trail last year. There was the star catch from the enemy, Ron Reagan Jr, the son of the brightest icon of modern Republicanism. There was the old liberal lion Ted Kennedy, and Barack Obama, the neoliberal lion of the Democrats' future. But this second evening of the Democratic convention belonged to Teresa Heinz Kerry.

The candidate's wife was appearing at a watershed in the campaign, 48 hours before the acceptance speech that could make or break John Kerry's White House bid - and at a time when George Bush seems to be regaining ground.

After weeks of being battered by Iraq and then the announcement of John Edwards as Mr Kerry's running mate, the President led his rival by 48 to 46 per cent in a new Washington Post/ABC News poll, reversing a trend of several weeks. Above all though, Mrs Kerry represented something absent this week, a frisson of unpredictability and a breath of controversy.

In fact, the controversy has already begun. Hours after telling a reporter from the conservative-leaning Pittsburgh Tribune-Review to "shove it", the equally conservative Boston Herald breathlessly unearthed a 1975 book about political marriages yesterday.

According to the book, Teresa, who was then married to the late Republican senator John Heinz, once declared that Edward Kennedy - now a close political ally of her husband - was a "perfect bastard" if he was maintaining his marriage to his former wife Joan merely to avoid upsetting the Catholic vote.

The Herald also dug up some remarks she made in 1976 to the effect that the Democratic party machine was "putrid". Yesterday, the Kennedy camp laughed off the fuss. But the episode only underlines how the extraordinary career of Mrs Kerry (who only formally left the Republican party in early 2003) will provide material galore for the Bush/Cheney campaign's muck-raking Opposition Research Department. But will they choose to use it, and if so, how?

For Republican campaign strategists, those are tricky decisions. Elections are not won and lost by first ladies, and attacking a potential one may be seen as unfair. None the less, first ladies are part of an overall presidential package. If voters can be discreetly made to feel uncomfortable with Mrs Kerry, that may be bad news for her husband in an election campaign as close as this one.

By accident or design, each presidential spouse seems a reaction to the last. The homely Barbara Bush with her twinsets and pearls was the antithesis of the Hollywood-tinged, fiercely protective Nancy Reagan. Then came the strong-minded, smart career woman Hillary Clinton. ("Heck, if you don't like him, don't vote for him," she told a TV interviewer in 1992, when questioned about her husband's alleged infidelities.)

Next up was Laura Bush, the opposite of Hillary. This Mrs Bush is a former librarian and schoolteacher, an unobtrusive home maker whose political contributions extend no further than a dewy-eyed gaze at her husband and uncontroversial speeches about her pet subject of education.

Now there is the very real possibility the next First Lady of the United States will be a daughter of Portuguese colonialists in Africa, owner of five homes and fluent in as many languages.

Mrs Kerry speaks her mind in breach of all the norms of political wife-speak. Her $500m-plus fortune renders her beholden to no one. Indeed, she has made clear that if her husband reaches the White House, she will continue her philanthropic and pro-environmental work. In her White House days at least, Hillary Clinton was a shrinking violet by comparison.

In terms of sheer exoticism, even Jackie Kennedy, with her cosmopolitan background, does not come close to Mrs Kerry. With her trace of an accent, her designer clothes and slightly world-weary manner, she has been described as resembling a famous European actress of a certain age.

If you live in Kansas (or even in large parts of Massachusetts) she must come across as a very foreign creature indeed. Almost certainly, the Republicans will seek to use that perception to reinforce their contention about her husband, that John Kerry is out of the American mainstream.

Last night, however, the unscripted, off-the-cuff Mrs Kerry was deliberately packed away, as she prepared to deliver her prime-time address to this most scripted of conventions. "Normally I don't have a text," she told an interviewer yesterday, "but this time I've been working on the speech for weeks." It would be personal, and she hoped, "an inspiration" to those who hear it.

But did she regret her words to the Pittsburgh reporter? "No, no one likes being trapped or misrepresented."