Barack Obama has come a long way since his first Democratic convention in Los Angeles eight years ago when, by his own account, he was down in the dumps and broke after being decisively beaten in his bid to win a seat in Congress.

On arrival at the airport, his American Express card was twice rejected and it took half an hour of negotiations to hire a car. Later, denied credentials to the convention floor, he spent a desultory few days watching speeches on TV screens and trying to follow friends into "skyboxes where it was clear I didn't belong" before going home early.

Four years on, still largely unknown and not yet even elected to the Senate, he burst onto the national stage with a speech at the Boston convention that electrified a party preparing grimly to annoint leaden John Kerry as its choice for the White House.

If some of those watching him back then thought that maybe - one day - he might himself run for president, few would have dared to predict that he would be arriving in Denver this week as the nominee and, according to Republican attack adverts, "the biggest celebrity in the world".

The inevitable tumult and triumphalism greeting him when he walks out in front of 75,000 people at the mile-high Invesco stadium on Thursday will, however, serve to obscure the great glaring gap in this rags-to-riches story: Mr Obama may not win.

Never mind that this should be a Democratic year with fully four-fifths of American voters saying the country is "on the wrong track", Mr Obama is running a long way behind his party. Polls show that a "generic Democrat" would have double-digit margin over a "generic Republican" but Mr Obama's summer lead over John McCain into a statistically insignificant 1.4 per cent.

For all the babble about him "making history" as the America's first black president, many voters are more concerned about saving their jobs or finding the money to pay for petrol and their mortgages. They cannot afford to make history, nor do they want it thrust upon them by wealthy coastal elites who idolise Mr Obama.

He won the Democratic nomination with a message of change carried by his own compelling oratory and symbolised by an inter-racial background as well as the enthusiasm of young white liberal and African American activists. But it should not be forgotten how he lost the final third of the primary to Hillary Clinton who painted him as an elitist, even as darker doubts were kindled about his religion and patriotism.

His campaign spent much of the summer patting itself on the back and preparing to fight the next general election battle with the same weapons that won the nomination. The Republicans were busy digging behind their own narrative about him being an untested and a somewhat sinister "unknown quantity".

Only in the past week has his team stirred from its self-regarding slumber and recognised that they have a proper scrap on their hands. Mr Obama has returned from his holiday in Hawaii with a fresh populist focus on America's failing economy, attacking Mr McCain's family wealth and his apparent failure to remember exactly how many houses he owns.

Although events are now being planned on a more "human scale", he will today today take the stage in Springfield, Illinois, for another trademark rally with his breathlessly-awaited choice of running mate. There is also the no small matter of his long-planned moment of mass adulation on Thursday but Mr Obama insists he will not be seeking to "dazzle" his audience, saying he dislikes his campaign being portrayed as "a rock concert".

The strategy this week will be about re-introducing him as the product of a "very American story" with family members and a series of ordinary voters lining up to pay testimony to his middle class origins or describe his down-to-earth qualities.

Little is being left to chance in Denver: in an exercise more reminiscent of the Beijing Olympics than the language of grass roots empowerment of his the campaign, protesters have been told they must demonstrate in a fenced-in parking lot outside the convention centre - with dozens of metal cages in a warehouse on the outskirts of the city set aside for those who misbehave.

Inside the convention, however, it will be hard to escape the fashionable chi-chi values of the liberal Democrats. Banners will be bio-degradable, delegates will be urged to offset the carbon costs of their travel, while 900 volunteers will stand at rubbish bins to ensure every scrap of recyclable trash is put in the proper container.

Mr Obama's gym-honed skinny frame sets him apart from the obesity that ripples across the waistband of Middle America and his convention's host committee has distributed "lean 'n' green" guidelines to Denver caterers. These implore them to strike fried food from menus and offer vibrant, nutritious meals which should include "at least three of the following colours: red, green, yellow, blue/purple and white".

It is not the image the Democrats need just now. Nor should they forget the last time the party held a convention in Denver, exactly 100 years ago when Williams Jennings Bryan - another politician known for his oratory - was chosen to run against the unpopular incumbent Republicans. He lost.

Times Recommends

• UN may halt 400-year-old 'freedom of the seas'
• Where the Rosetta belongs can’t be set in stone
• Gas deal on hold, but Ukraine may pay in the end