If John Kerry becomes president, his wife Teresa Heinz Kerry might at last be said to have married well. As one of the richest widows on the planet, she was the real catch, until now.

She is Kerry’s greatest asset in more ways than one, lending him a dash of devil-may-care spirit to match her $550m fortune. Furthermore, she is “definitely sexy . . . very earthy, sexy, European”, as Kerry once cooed.

Marriage to a wild card like Heinz, who was born in colonial Mozambique to a Portuguese family, has made the previously formal Democrat more “loosey goosey”, says a family friend.

It is just as well. Kerry has had to grin and bear her depiction of her hugely rich first husband, John Heinz III, the ketchup heir and Republican senator, as the “love of my life” and watch her yawn and fiddle through his speeches on the campaign trail.

Heinz Kerry, 65, has let slip that she loves Botox, prompting rumours that her once-haggard husband has had his forehead plumped. She also insists, despite this denials, that the war hero still has nightmares about Vietnam. Kerry has been in therapy, she admitted to his chagrin. For a lady who power lunches in Washington and New York there is nothing odd about seeing a shrink, but it might not play well in conservative states.

Two big egos do not make for an easy marriage. “They fight,” says a Washington friend of the couple. “They’re two strong-willed people who occasionally get irritated with each other.”

There is no doubting who has the upper hand financially — Kerry signed a pre-nuptial agreement. “Everybody has a pre-nup,” Heinz Kerry blurted out, displaying a blithe insouciance about the lifestyle of non-millionaires. With three sons from her first marriage, she explained: “You’ve got three kids with somebody else, you’ve got to have a pre-nup.” Kerry, a Catholic, also obliged her by asking his first wife, Julia Thorne, for an annulment of their marriage. As the mother of Kerry’s two daughters, Thorne called the demand “devoid of any sense of the humanity of what this means to me and the children”. They split up for six years before their divorce in 1988.

During his semi-bachelor years Kerry was linked to a succession of blondes, including Morgan Fairchild and Catherine Oxenburg. He met Heinz Kerry briefly in Washington with her first husband, but only came to know her at the 1992 Earth Summit in Brazil. By then she had been widowed for a year and had inherited the baked bean millions.

On their first date Kerry took her on a moonlit tour of the Vietnam memorial at Arlington cemetery, where he showed her the names of his fallen comrades. They lived together for a while before marrying in 1995.

She remained a Republican until last year, when she claimed the party had deserted the centre ground. “I love George, Big George,” she has said of the elder Bush. “He was so sweet and wonderful to me when Jack (Heinz) died.” For the son she feels contempt.

As she jets around the primaries in her private plane, Heinz Kerry shows every sign of enjoying the spotlight. She is almost as much a star of Kerry’s campaign as the candidate.

She does not go in for Nancy Reagan-style adoring gazes, nor does she offer the political partnership of the Clintons.

“When Heinz was senator, a lot of effort went into keeping Teresa from expressing her opinions,” said a veteran Republican campaigner. She is off the leash now, but is trying to muzzle herself. She says, regretfully: “I’ve learnt not to tell jokes.”