COMPLACENCY kills campaigns," insisted Mark Mellman, a Democratic strategist and John Kerry's pollster in the 2004 presidential race. "Winners," he added, "always run like they are behind."

COMPLACENCY kills campaigns," insisted Mark Mellman, a Democratic strategist and John Kerry's pollster in the 2004 presidential race. "Winners," he added, "always run like they are behind."

With just three days to go before polling day in America, Barack Obama and his campaign team are desperately trying to keep up the frenetic pace as they enter the last lap, aware that the finishing line is tantalisingly within sight.They know they must get the Democratic vote out and stave off the merest suggestion that victory is in the bag; that way leads to John McCain sneaking a narrow victory for the Republican cause.

While on the stump in Florida this week, the 47-year-old senator from Illinois exhorted his adoring audience against counting chickens: "We can't afford to slow down, or sit back, or let up, for one day, for one minute, for one second in this last week. Not now. Not now. We've got to work hard."

This thinking was clearly behind Obama's decision to go ahead with an outdoor rally in Pennsylvania despite some horrendous weather. The thousands who braved the elements had to endure horizontal rain, a bitingly cold wind and ankle-deep mud. Interestingly, just 50 miles away and suffering with the same climatic conditions, McCain decided to cancel his rally.

Recriminations already appear to be affecting the Republican camp. Some of its members have defected to the Democrat cause, earning themselves the title of "Obamicans"; the most notable is Colin Powell, ex-US Army general and George W Bush's former Secretary of State.

As more statistics confirm that America is sliding into recession, "the economy, stupid" is playing into Democrat hands despite McCain's central assertion that his opponent's financial policy is "from the far left of American politics" and that Obama would raise ordinary Americans' taxes. Yesterday, the 71-year-old Arizona senator, rolling through Ohio on his Straight Talk Express bus, was insistent that he was closing the gap on his Democrat rival and that there was all to play for. "We're coming back," McCain asserted.

And yet, despite Obama's understandable guard against complacency, late come-from-behind wins are rare in presidential races. Only twice in the past 14 elections has a candidate lost the popular vote after being ahead about a week before the election: Democrat Jimmy Carter in 1980 and Bush in 2000 - although, hanging chads aside, he won the electoral college vote.

As the election day nears, Obama is ahead of McCain in most US national polls, while most state surveys show him running strong in traditional Democratic states and leading in some that Bush won in 2004, including Ohio, Colorado, Nevada and Virginia. That makes a path for a McCain victory difficult to see, although Mellman pointed out that all those polls assumed every Obama supporter would turn out to vote and every volunteer would do what it took to turn out the Democratic vote.

Reaffirming his warning against taking victory for granted, Obama told his Florida rally: "Don't believe for one second in these polls. Power concedes nothing. We are going to work over the next five days like our lives depended on it. We're going to have to struggle."

The Scottish comedian Craig Ferguson, who now hosts The Late Late Show on the US television network CBS, was one of those who warned that the left sometimes has the knack of snatching defeat from the jaws of victory. "Obama is so far ahead now," he said, "it seems the only way he can lose is if his supporters screw it up. But aha! Obama's supporters have a secret weakness. They're Democrats."

Even among die-hard Democrats who see their man eight, nine or 10 points ahead in the polls, there is that gut-wrenching feeling that America, being the conservative place that it is, might just decide on Tuesday to stick with the devil it knows rather than take a historic leap in the dark.

It is as much Obama's background as his policies that cause concern within Middle America. The first-term Illinois senator spent much of this year's party convention trying to convince the doubters about his American credentials. Many of the speeches were preceded by mini-biographies showing how he was just a regular all-American guy like those in the audience and those watching proceedings at home on TV.

Born in Hawaii to a white Kansan mother and a black Kenyan father, he shot to fame with a speech to the Democratic National Convention in 2004 when he declared: "In no other country on earth is my story even possible," and noted: "There is not a liberal America and a conservative America; there is the United States of America. There is not a black America and a white America and Latino America and Asian America; there's the United States of America."

His father abandoned the family after just two years and the young Obama was raised by his teenage mother and his white grandparents. Having won a scholarship to attend a prestigious school in Honolulu, he studied at Harvard Law School and, spurning a well-paid city legal post, opted instead for civil-rights work in the run-down south side of Chicago.

He was elected to the Illinois senate in 1996 but suffered a crushing defeat in 2000 when he ran for the US Congress against an incumbent Democrat. Nevertheless, in 2004 he was elected to the US Senate.

The candidate's most famous book, The Audacity of Hope, published in 2006, outlined his political philosophy, which was moulded by the Midwestern values of his mother and grandparents. Brisk sales helped make Obama a millionaire.

Running the gauntlet of a long and bitterly fought presidential campaign is a searing experience in itself; the shakiest moment for the Democrat candidate came in the wake of the incendiary racial language of his one-time friend, the Reverend Jeremiah Wright. Obama, known for his cool reflectiveness, rode the storm successfully - and also appears to have learned that, as a potential President, he might not have the luxury of having time to examine all the angles on every policy. As one adviser observed: "He has learned to trust his gut. He wasn't so confident in his instincts last year. It's been the biggest change I've seen in him."

To his fans, he is an inspiring once-in-a-generation politician like John F Kennedy, but to his critics he is little more than a celebrity with a thin resumé, an eloquent speaker who preaches "naive" foreign policies and advocates "socialist" tax-raising economic policies. With the military and diplomatic conundrums posed by Iraq, Iran and Afghanistan, the still-present threat of terrorist attacks, the effects of the credit crunch, the new competition from Russia, India and China and the challenges of global warming, the 44th President of the United States is going to have his work cut out.

Domestically, a President Obama would have to lead the home of the credit crunch out of recession with the promise of tax cuts for 95% of working families, a boost to small businesses by eliminating capital gains tax, and heavy investment in green technology - dubbed, because of its potential scale, the "Apollo Project". In foreign-policy terms, a President Obama wants to see a phased withdrawal of troops from Iraq but an increase in forces in Afghanistan.

As for relations with Britain, the Democrat candidate will no doubt uphold the "special relationship", pragmatically noting how the UK still has spheres of post-Empire influence which America does not, particularly on the Indian sub-continent. Plus, of course, Obama has family in England.

Yet for all the various issues, domestic and foreign, in the presidential contest, there is one imponderable underlying it: race.Just how big the so-called Bradley Effect will be - where white voters tell pollsters they will vote for a non-white candidate but, come election day, do the opposite - is unknown.

A recent survey in Texas showed that, despite all the information about his Christian background, almost 25% of respondents believed Obama to be a Muslim. Last month, two white supremacists were arrested over an alleged plot to assassinate him; this week, two people were held for supposedly hanging a life-sized likeness of him from a tree on the campus of Kentucky University.

These incidents might be put down to misguided, feckless individuals having nothing better to do - yet electing the first black President is something about which even some liberals might have brief second thoughts.

Were McCain to sneak victory from the jaws of defeat, expect to hear more about the Bradley Effect as inevitably the case will be put that a narrow Republican victory was down to racist fears. Yet if Obama, campaigning across the Midwest yesterday, holds his nerve, keeps his foot on the pedal and wards against complacency, then, come Tuesday, history could well be made.

The skinny guy with the funny name - as the Democrat candidate has described himself - could end up being the first black leader in the White House.

A journey almost as fascinating as her husband's

Barack Obama's bid to become America's first black President has been gripping - but almost as fascinating has been his wife's journey through the campaign.

Michelle Obama, 44, has made a powerful impact but has often been the target of conservative attacks.

Born Michelle LaVaughn Robinson, she has described herself as "Chicagoan through and through". She specialised in marketing and intellectual property at the Chicago offices of the law firm Sidley Austin Brown & Wood, where she met her future husband in 1989 when he interned during a summer break from law school.

They have two young children, Malia and Natasha. Earlier this year, the couple allowed the cable show Access Hollywood to interview the girls as Malia celebrated her 10th birthday, but later questioned their decision. "I don't think it's healthy and it's something that we'll be avoiding in the future," Barack Obama said.

The fire aimed at Michelle has also affected him. Some Republicans questioned her patriotism after her comment that her husband's campaign had made her proud of her country "for the first time". In the furore that followed, the Democrat candidate told Republicans to "lay off my wife".

One of the most controversial episodes involving the couple was when the satirical magazine The New Yorker featured a cover depicting Barack as a Muslim and Michelle as a terrorist. "The New Yorker may think their cover is a satirical lampoon of the caricature that Senator Obama's right-wing critics have tried to create, " said Obama campaign spokesman Bill Burton at the time. "But most readers will see it as tasteless and offensive."