Barack Obama has revealed how he plans to deploy the queen of American daytime television in an audacious raid on Hillary Clinton’s core support among women voters in the Democratic presidential contest.

Mr Obama announced yesterday that Oprah Winfrey would campaign alongside him in Iowa, the crucial first state that kicks off the nominating process on January 3, before taking her to the other key early battlegrounds of New Hampshire and South Carolina.

The billionaire television show host, rated the second-most-influential woman in the US behind Mrs Clinton, has already demonstrated her power to sway sentiments among viewers, with her book club catapulting obscure novels into the bestseller lists. Mr Obama — who trails Mrs Clinton by a wide margin among women voters in national opinion polls — has suggested that Ms Winfrey’s support “means that I may get a hearing in certain quarters”.

Tomorrow his campaign will unveil “Women for Obama Leadership Committees” in a clutch of states holding primary elections on February 5, or Super Tuesday, which may decide who wins the nomination.

His strategists believe that he can win support from cautious female voters worried that Mrs Clinton is unelectable. A new poll last night suggested that she trails the top five Republican presidental candidates in head-to-head match-ups. Such vulnerability is particularly true in Iowa, which has never backed a woman for statewide office or Congress.

A recent poll in the state, where Mr Obama held a discussion on health policy with women panelists on Sunday, showed that he had edged ahead of Mrs Clinton for the first time and had closed the gap among women voters. Last night he appeared in a TV interview suggesting that Mrs Clinton would lose her front-runner status if she failed to beat him in the Iowa caucuses. “You guys have been measuring the curtains for a while,” he said, “you telling me she can get away with not winning Iowa?”

In an increasingly intense battle with Mrs Clinton, he also used the interview to take aim at her claim to be more experienced because of her eight years as First Lady.

“There is no doubt that Bill Clinton had faith in her and consulted with her on issues, in the same way that I would consult with Michelle, if there were issues,” he said. “On the other had, I don’t think Michelle would claim that she is the best qualified person to be a United States senator by virtue of me talking to her on occasion about the work I’ve done.”

Mrs Clinton will today seek to bolster her position in Iowa by campaigning with her husband, Bill, the former President. The couple are reported to be “setting up camp” in the state for the next 40 days. She spent much of the weekend criticising Mr Obama’s foreign policy credentials and his “kind of confusing” healthcare policy.

The spat among Democratic candidates is positively polite compared with the wildly unpredictable race for the Republican nomination in which the two front-runners, Rudy Giuliani and Mitt Romney, have exchanged personal insults for the first time.

Mr Giuliani, who leads nationally but trails Mr Romney in the earlyvoting states, mounted a ferocious criticism of the former Massachusetts Governor’s record on taxation and law enforcement.

That gave Mr Romney the chance to bring up Bernie Kerik, Mr Giuliani’s close friend and former New York police chief, who was indicted this month. He also linked Mr Giuliani to abortion and gay rights, compared his ethics to those of Mrs Clinton, before an aide went even further, branding him nasty.

Campaigning in New Hampshire on Sunday with his wife of 39 years, Mr Romney made an implied reference to Mr Giuliani’s three marriages, as he spoke about the former Mayor of New York’s admission that he was “not perfect”.

Mr Romney said: “Everybody makes mistakes, but not everybody asks to be president of the United States.”

Mr Giuliani’s campaign manager was later quoted as describing Mr Romney as a “mediocre one-term governor”.

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