Leading article: An exciting choice that reveals the disillusion of voters

After more than 50 contests over five enthralling months, the United States' primary season came to an end almost where it began, in the farming heartland of the northern states. After prevailing in Montana and losing in South Dakota, Barack Obama claimed the victory that really mattered in the very same cavernous hall in St Paul, Minnesota, where the Republican Party will hold its nominating convention in three months' time. It was the Senator's way of announcing his win and at once taking the battle to the adversary.

That this year's Democratic nomination would make history was evident as soon as Barack Obama established himself as the candidate for Hillary Clinton to beat. As the first African-American with a realistic chance of reaching the White House, he carries the hopes of millions: not just the millions of black American voters whose support he increasingly garnered in the primaries, but the hopes of those many Americans whose ambition is for their country to be colour-blind.

Perhaps his greatest achievement through the primaries, though, was to set himself above the destructive politics of race that have for so long poisoned American public life. He campaigned as mainstream candidate, as a US Senator, whose career and ambition gave him as much right as any other American to compete for the presidency. This turned out to be as shrewd a calculation as it was admirable.

With hindsight, the explanation of Barack Obama's victory seems simple: he emerged increasingly as the most impressive candidate. He is the one who drew ever greater numbers to school halls across the country. He is the one who left audiences spell-bound. He is the one who seemed most hungry for the job, clearest about where he stood, and most comfortable in his own skin. He is also the candidate who grew the most in stature as the campaign progressed. The length of this primary season, however gruelling, worked to his advantage.

It is usually said that elections are lost rather than won. And it is true that five months ago, the nomination was seen as Hillary Clinton's to lose. It was she who had the fullest war-chest, and she who had the most impressive contacts book. Her front-runner status, however, and her past as a controversial First Lady burdened her with influential enemies. Unexpected early losses initially left her support team in disarray and prompted a re-think of her campaign strategy.

What is more, her husband – someone whose political instincts were assumed to be second to none – proved more of a liability than an asset. As more and more ethnic minority voters flocked to Mr Obama, it was he who demeaned himself by resorting to innuendo and the race card. In time, it is the reputation of Bill Clinton that could be the big loser from this campaign.

In the end, Mrs Clinton's emerges with more credit than at one time looked possible. Her increased confidence on the stump, her strength of will and her ability to fight back combined to show a convincing politician. And her campaign demonstrated beyond any doubt that a woman can be a realistic candidate for the US presidency. But her sense of entitlement, her obstinacy in the face of defeat and the damage she has caused her party during such a fiercely contested campaign all mean that her offer to become Mr Obama's deputy should be rebuffed. It would send all the wrong signals for a presidential candidate who is such a powerful symbol of change.

Ultimately, this was a campaign that was not lost by Hillary Clinton, but won by Barack Obama. His decision to campaign from the high ground, above grubby racial politics, has been rewarded, something that should be noted by democratic politicians around the world. He turned his relative youth and the brevity of his top-flight political experience into advantages with an electorate jaded by eight years of failure under George Bush and the prospect of another political dynasty. His call for change, however unspecific, struck a chord. It was a change that radiated from his whole manner and his very being.

Not for the first time American voters have chosen the bolder course: youth over age; instinct over experience; change over the status quo. This openness to new ideas and individuals is a laudable national characteristic. But it also a reflection of the depth of disillusionment in the United States today. Barack Obama, no less than Bill Clinton in his day, is the candidate who best represents hope to fellow Democrats.

On the day that a presidential candidate clinches the nomination, the whole nature of the contest changes. Now Mr Obama has to appeal not just to habitual Democratic voters, but across the party divide. He has his work cut out. The "swing" states that he most needs to win are, for the most part, those where Mrs Clinton scored her big victories. John McCain is already courting these voters for his particular brand of Republicanism.

In Mr McCain, Barack Obama faces a uniquely challenging opponent. Age against youth and instinct against experience will both be elements of the contest. But John McCain is the one – among all the Republican hopefuls – who remains least contaminated by the debacle of the Bush presidency. For a Republican he is socially more progressive (though, as a candidate, he has at times to hide this). Like Mr Obama – whose embryonic protectionism, we hope, will be a relic of the primaries – he is internationalist in outlook, favouring alliances, joint action, and green politics. Like Mr Obama, too, he is a fully-formed character, whose ideas and personality are all of a piece.

Early differences, which are bound to be more sharply delineated as the campaign goes on, centre on health care, the role of the state and Iraq. To win over the undecided centre, Mr Obama will need to choose his advisers and his running-mate wisely. But he is in with a chance in an election that promises to be as exciting and absorbing as the primary season before it. We will watch with enthusiasm, and not a little envy, as American voters make their choice.

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