Seventeen months after she sat regally in her New York living room and calmly declared: “I’m in and I’m in to win,” Hillary Clinton stands on a stage in a stifling hot shed in South Dakota, coughing and spluttering, as her daughter, Chelsea, grabs the microphone from her hand to take over the show.

“A long campaign,” the former First Lady chokes out between sips of water. Her husband, red-faced and exhausted — and having just apologised for another angry outburst in front of reporters — looks on wistfully at the final rally of his wife’s presidential bid, an endeavour that has been transformed from an inevitable juggernaut into a costly train wreck.

It was an extraordinary moment, exactly five months after the first contest in Iowa, to see the former First Family in the dying moments of the longest primary campaign in history, a gruelling journey across America that was meant to end in a Clinton restoration and has instead bought a very different inevitability: defeat at the hands of Barack Obama.

Earlier in the day in the South Dakotan town of Milbank, Mr Clinton all but threw in the towel, even as his wife was insisting at an event near by that she was still the best candidate to defeat the Republican John McCain in November.

“This may the last day that I’m ever involved in a campaign of this kind,” Mr Clinton said, a man who for weeks has been holding seven or eight events a day in an increasingly desperate bid to rescue his wife’s candidacy and his own legacy. “It has been one of the greatest honours of my life to be able to go around and campaign for her for president.” When his wife declared her candidacy in January 2007, she was the formidable front-runner already hoovering up money and endorsements, and Mr Clinton was still the Democratic party’s rock star. Today he has to endure the painful reality that many African-Americans have turned their backs on him, and allegations that his tirades and behaviour contributed to his wife’s demise. Having raised a staggering $214 million (£107 million), her campaign is near defeat and $30 million in debt.

Only hours before this event in the dusty and windswept fairgrounds of Sioux Falls, Mr Clinton had been unable to control himself again. Responding to a new article in Vanity Fair that suggests his heart bypass surgery four years ago has altered his personality and made him chronically angry — and insinuations that he is still a serial adulterer — the former President called the reporter a “scumbag” and a “slimy guy”. Later he issued a statement saying that he was “understandably upset about an outrageously unfair article”, but his language “was inappropriate and he wishes he had not used it”. In this final day of campaigning, Mrs Clinton was still defiant, still giving, as she has done for months, an impressive and detailed stump speech full of uplifting prescriptions for healthcare, taxes and energy independence. Yet there was a sense of a woman with her fingers in a leaking dam, straining to halt the impending flood of super-delegates to her rival. Even as she spoke in Sioux Falls, several of her Democratic Senate colleagues were meeting behind closed doors in Washington to plot the endgame by planning a mass endorsement for Mr Obama.

At two events she became convulsed by coughing fits. At one she got the name of the mayor wrong. In Yankton she lost her voice and had to leave the stage. Chelsea again took over, the reluctant campaigner of Iowa now a star in her own right. During the day Mrs Clinton’s event advance team was laid off. Campaign staff were urged to hand in expense receipts. Young aides were talking about vacations. Several volunteers, amid a slightly hysterical fin de siècle atmosphere, gave Oscar-like speeches listing all the states they had visited.

Yet the event also emphasised how galling this race has become for the Clintons. Mrs Clinton now argues that more people — nearly 18 million — have voted for her than for Mr Obama. She has won most of their contests since February 20. There were queues stretching hundreds of yards in Sioux Falls, and new polls showing her suddenly leading her rival in South Dakota.

“I’m not up here because I have the best mum,” Chelsea told the crowd. “It’s because I fundamentally know she will be the best president.” A sudden gust sent hundreds of “Get Out the Vote” slips flying into the South Dakota sky. Soon, the Clintons were gone too, heading back to New York to plan the concession.

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