Democrat handlers rein in Mrs Kerry, the campaign's unguided missile

John Kerry, the Democrat Senator from Massachusetts, would bring many things to the White House should he win the 2004 presidential election: sharp-end experience of war from Vietnam, a deep knowledge of public policy, and an abiding interest in foreign affairs. But most intriguing of all, he would also bring his wife.

There have been several notable First Ladies in modern times: Eleanor Roosevelt, Rosalynn Carter and Hillary Clinton, to name but three. But in terms of speaking their minds, none can hold a candle to Teresa Heinz Kerry.

Indeed, until the emergence of Howard Dean, a dark horse candidate, she was the story of a Democratic campaign which never quite caught fire.

The candidates expatiated about Iraq, budget deficits and soaring health-care costs. Ms Heinz Kerry, by contrast, was making such unpolitical admissions as that she has made a pre-nuptial agreement with her second husband ("every-one does pre-nups") and that she has Botox treatment.

In a now famous interview with American Elle magazine in May, she declared that she would "maim" any husband who misbehaved, adding that they should resist temptation if she could ­ though "maybe I'm into 18-year-olds". That was a joke, interjected a nervous aide.

Jest or otherwise, this most definitely is not First Lady talk. Should her husband win the nomination and then the White House, do not expect a Pat Nixon or Laura Bush, gazing in frozen adoration as their spouse delivers a speech they have heard a hundred times. Indeed, Ms Heinz Kerry once called the prospect of living in the White House "worse than going to a Carmelite convent".

The Kerry marriage is a study in contrasts. He comes across as serious and stiff, remote and lacking in spontaneity. She is authentic and unfiltered ­ some would say an unguided missile ­ the delight of journalists and nightmare of campaign managers. There are reports, denied by aides, of a ferocious temper.

Beyond the sassy talk, however, is a woman who is a complicated mix of present and past, defined in public by marriages to two prominent US senators, but with a cosmopolitan background all of her own (she speaks five languages) that makes the late Jacqueline Kennedy look like a small town midwesterner.

She was born Maria Teresa Thiersten Simoes-Ferrara, the daughter of a Portuguese doctor in colonial Mozambique. She met her first husband, John "Jack" Heinz, heir to the family food empire, in the mid-1960s in Geneva, where she was a young interpreter for the United Nations.

"My family makes soup," he told her on their first encounter. He made his mark not as a CEO, but as a popular Senator from Pennsylvania, practising a brand of centrist, noblesse oblige Republicanism all but extinct today.

Mr Heinz ­ the man she still refers to as "the love of my life" ­ died in a plane crash in Philadelphia in 1991, and she inherited a fortune estimated today at $550m (£340m). But although Forbes magazine ranked her 391 in its list of America's wealthiest people, that wealth will almost certainly not be available to finance her second husband's campaign. She married John Kerry in 1995, but only later added Kerry to her name. Not until January did she formally change her party affiliation from Republican to Democrat ­ partly out of loyalty to her candidate husband, but also because of the party's more right- wing and intolerant policies. But the woman beneath has not changed.

For Mr Kerry she is "a great asset," a woman who is "incredibly loving, fun, zany, witty ... very earthy, sexy, European." But as John Heinz was also aware, a distinctly loose cannon.

In one sense, Ms Heinz Kerry is well suited for the First Lady's role, with its traditional focus on good deeds. She runs the $1bn Heinz philanthropic endowment, and has won awards for her humanitarian work. She is also an environmental activist ­ indeed, she first got to know her current husband at the 1992 Earth Summit in Rio, to which both were delegates.

First, however, he must win his party's nomination, and then defeat the present President, George Bush. As the campaign intensifies, his aides ­ well aware that a gaffe could swing what promises to be a very tight race ­ are less concerned with promoting his wife's undoubted virtues than practising damage control.

Sadly for reporters, the handlers are closing around Ms Heinz Kerry. Already she has her own spokeswoman, a former journalist, and the spate of media interviews has slowed to a trickle. But she is unlikely to be silenced completely.

"You'd never call the husband of a female politician impolitic because he had opinions," she told Vogue magazine, perhaps unmindful of the late Denis Thatcher. "At my age I'm entitled to have strong beliefs. I'd be a ninny if I didn't."