Hillary Clinton's comeback victories in Ohio, Texas and Rhode Island were based on a newly aggressive strategy to attack Barack Obama directly and from all directions, a plan that was mapped out by her husband, Bill, who now exerts enormous influence on the inner workings of her campaign.

The “throwing the kitchen sink” strategy was aimed at knocking Mr Obama off his stride, to sow doubts about his fitness to be commander-in-chief, to question his ethics and to convince enough voters that the messenger of hope and change was too risky a bet to prevail against the Republican attack machine leading up to November. At the same time, Mrs Clinton stopped focusing on the uninspiring message that she was a hard worker. Instead, she told Ohio and Texas repeatedly, she was a fighter.

There was little margin for error after Mr Obama's 12 straight victories in February but the results were startling. On Tuesday night Mrs Clinton resoundingly reclaimed her base of women and blue-collar voters. Late deciders, who have backed Mr Obama overwhelmingly in previous contests, turned out for the former First Lady by a margin of two to one. Mr Obama beat her among every demographic in his 17-point landslide victory in Wisconsin on February 19. In Ohio, she won union households 56 per cent to 43; nearly 60 per cent of women; and for the first time in weeks, beat Mr Obama among white men.

Mrs Clinton was also helped by three pieces of bad timing for Mr Obama that helped to throw him on the defensive in the days before Tuesday's contests: a late-night comedy show lampooning the national press for fawning over him; a leaked memo suggesting an aide had told the Canadian Government that his tough talk against free trade was political posturing; and the opening of the corruption trial of Antoin “Tony” Rezko, a former Obama fundraiser.

After effectively - and very publicly - hijacking his wife's campaign in January, a move that saw him red-faced and aggressive before the cameras, accused of racism, and raising the spectre of a co-presidency, Mr Clinton's behind-the-scenes influence in recent weeks has been crucial to reviving his wife's campaign.

The former President's instincts have long been to take on Mr Obama aggressively but when he tried to do it himself it backfired. For the past month, he has campaigned tirelessly on his wife's behalf but away from the limelight and relentlessly on-message. Meanwhile, with Mrs Clinton's new campaign manager Maggie Williams, he is having a far bigger say in strategy, while using every spare moment to telephone super-delegates and donors to keep them on board.

The “turning point”, as Doug Hattaway, one of Mrs Clinton's spokesman, said at her victory rally on Tuesday night, came with the airing five days before the primaries of a television advertisement attacking Mr Obama's fitness to handle a foreign policy crisis. The emotive commercial asked voters who would they like answering the White House crisis phone at 3am while their children were asleep.

“It reminded people of the stakes in this election,” Mr Hattaway said.

“Expect more of the same in Pennsylvania.” Mrs Clinton also had 30,000 volunteers in Ohio and 45,000 in Texas, evidence that she can beat Mr Obama when she gets boots on the ground.

The passionate crowds that surround her are also often overlooked.

In the days before Tuesday's contest Mrs Clinton and her aides repeatedly raised questions about Mr Obama's links to Mr Rezko. She attacked her rival for failing to hold hearings as chairman of the Senate Foreign Relations Committee. The leaked trade memo was an unexpected boon, allowing the former First Lady to accuse Mr Obama of lying about the issue to voters in economically depressed Ohio, where opposition to the North American Free Trade Agreement (Nafta) is fierce.

Meanwhile, the US press entered a period of introspection after Mrs Clinton used the Saturday Night Live sketch - in which a lovestruck debate moderator asks an Obama impersonator if he was comfortable enough - to accuse the Fourth Estate of giving her rival a “free pass”. At a press conference on Monday Mr Obama was peppered with questions about Mr Rezko, Nafta, and his credentials to be commander-in-chief. He brought the session to an abrupt close, saying as he left: “C'mon guys, I just answered, like, eight questions.”

Despite Mr Obama's bad week, Mrs Clinton's staff were still uncertain. Phil Singer, a spokesman, said he would shave his head if she won three contests. Yesterday Mr Singer was happy - but bald.

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