Hillary Clinton has reasserted her authority over her Democratic rivals with an aggressive performance in the latest presidential debate.

After a troubled fortnight in which a defensive Mrs Clinton has fended off questions about her honesty and electability, she moved forcefully on to the front foot. She accused Democratic rivals of throwing mud at her simply because she was ahead in the polls.

The rivals, Barack Obama and John Edwards, were booed by some in the crowd when they went on the attack. The result was that Mrs Clinton appeared to steady the ship. The first words out of a senior aide’s mouth yesterday were: “She’s back.”

Mrs Clinton, Mr Obama and Mr Edwards all return to the critical first nominating state of Iowa in the coming days, where they are locked in a statistical tie. But Mrs Clinton heads there with the state’s influential Des Moines Register declaring that she easily won the Las Vegas debate – a welcome boost in a state where her campaign was forced to admit recently that it had planted questions at her events.

For the first time in months the Democratic race appears truly competitive. Mrs Clinton’s troubles began at a debate on October 30, when she was accused of giving dishonest answers. At the same time Mr Obama, whose campaign had appeared listless and fading, is generating fresh excitement, especially after the best speech of his campaign to an audience of 9,000 Iowans last weekend.

Mrs Clinton’s performance on Thursday night, before a friendly audience in Nevada, where she is popular among Democrats, was thus a test of how she would react to the first true pressure of the campaign.

She attacked her rivals for the first time, accusing them of adopting tactics out of the Republican playbook, after Mr Obama and Mr Edwards continued to try to paint her as cynical and inauthentic. “What the American people are looking for now is straight answers to tough questions, and that is not what we’ve seen out of Senator Clinton,” Mr Obama said.

Mr Edwards said: “She says she will bring change to Washington, while she continues to defend a system that does not work.” Mr Edwards also accused Mrs Clinton of trying to have it both ways on a host of issues.

“I’ve just been personally attacked again,” Mrs Clinton broke in. “I don’t mind taking hits on my record on issues, but when somebody starts throwing mud at least we can hope it’s accurate.”

She added: “They’re not attacking me because I’m a woman. They’re attacking me because I’m ahead.” Later, when Mr Edwards and then Mr Obama went on the attack again, they were booed by some in the audience.

The three rivals are acutely aware of how large Iowa looms in the campaign. A victory by Mr Obama or Mr Edwards on January 3 could alter the dynamic of the race significantly. A victory there by Mrs Clinton could end it almost before it begins.

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