Hillary Clinton has been pacing a stage in the Winnacunnet High School gymnasium for nearly two hours, answering dozens of questions from a New Hampshire crowd with humour, compassion and a flawless command of detail.

A few hours earlier, 25 miles (40km) north in Rochester, her husband, Bill, talks to about 220 people in Bow High School, reminiscing about the golden days of his presidency, and explaining why his wife is an exceptional White House candidate because she has a plan for everything.

Mrs Clinton's direct engagement with the gym crowd is part of a new Hillary, unveiled after her defeat in Iowa. Yet by the time she has finished, half her audience has gone home. Mr Clinton, who has always played to sell-out crowds in New Hampshire, has a thick cold and is staring out on a two-thirds empty gymnasium.

For a couple that have dominated Democratic politics for nearly two decades, their appearances across New Hampshire have all the feel of an increasingly desperate last stand: not only against the looming tidal wave of Barack Obama, but also against the powerful forces threatening to consign them to history in a party they have ruled unopposed for a generation.

Trying to rebound from defeat in Iowa on the eve of New Hampshire's primary - where polls have her trailing Mr Obama by double digits - Mrs Clinton is scrambling for survival, while her husband, campaigning on her behalf, is fighting to save his legacy. It is a stunning new turn in the 2008 presidential race in which Mrs Clinton appeared to be an unstoppable political force only six weeks ago.

In a comment that revealed just how besieged and frustrated the Clintons suddenly feel at their apparent inability to halt Mr Obama's momentum, the former President told a crowd on Sunday night: "I'm sorry. I can't make her younger, taller, male."

Inside the campaign, recriminations have begun. Aides are calling donors and supporters to keep them on board. Discussions are taking place about how Mrs Clinton should respond if she loses New Hampshire badly, a result that would gravely endanger her candidacy. In South Carolina, a crucial primary on January 26, there are signs that African-American voters - half the Democratic primary electorate - are overcoming their doubts about Mr Obama and flocking to him.

Mrs Clinton has reinvented her campaign in New Hampshire. The question-and-answer sessions have replaced her stump speech. She is holding intimate discussions with small groups of young and independent voters, and has an "Ask Hillary" feature on Facebook. Mr Obama travels the state with his grandiloquent message of change - and takes no questions; Mrs Clinton is plugging a message of "rhetoric versus results".

At Winnacunnet High School, she is impressive, her command of policy peerless. She reminds her audience of the economic boom during her husband's presidency. She talks about $3,500 tax credits for families paying university costs, relief for small businesses, education reform.

And yet, the crowd begins to drift away. It is getting late. but even before she appeared her aides seemed to be creating a false impression of an overflow crowd. The doors to the gym were locked early - even though another 200 people could have easily fitted in the room - and 300 were redirected to another auditorium where they listened to Mrs Clinton on loudspeakers.

Andrew Smith, a political science professor at the University of New Hampshire, explains Mrs Clinton as the "eat-your-vegetables" kind of candidate, pointing to her experience and telling voters what will be good for them. Mr Obama is offering "three kinds of ice-cream".

The Clintons have always had a special relationship with New Hampshire. In 1992 Bill Clinton, facing allegations of adultery and Vietnam draft dodging, came second, and with Hillary at his side proclaimed himself "the comeback kid". Now, as they try to become the comeback couple, Mr Clinton is stealing a page from the Republican playbook used against him 15 years ago, telling crowds that Mr Obama is too young and too untested to be trusted with the presidency.

Yet for all his skills as a campaigner, even he is struggling to solve the central conundrum of his wife's White House effort: for all her poise and policy acumen, she will never have his dazzling ability as a campaigner.

The Clintons have been in extraordinarily tough fights before, and prevailed. Their strategists are now focusing on the Nevada caucuses in a week's time, and then on February 5 - Super Tuesday - when 24 delegate-rich states vote, including California and her home state of New York.

At a stop in Portsmouth yesterday, Mrs Clinton was asked by a follower: "How do you keep upbeat and so wonderful?" Her voice breaking and with tears in her eyes, she replied: "This is very personal for me. It's not just political, it's not just public. Some people think elections are a game, lots of who's up or who's down, [but] it's about our country."

By Tim Reid, The Times, January 7, 2008