Barack Obama and John McCain are barnstorming across America's battleground states today as one of the most costly, dramatic and momentous elections in US history enters its final hours with every poll suggesting Mr Obama is poised to become his country's first black president.

The 47-year-old first-term senator is leaving nothing to chance, however, as he jets from Florida to North Carolina to Virginia.

"After decades of broken politics in Washington, eight years of failed policies from George Bush, and 21 months of a campaign that has taken us from the rocky coast of Maine to the sunshine of California, we are one day away from change in America," he told tens of thousands of chanting, screaming supporters in Jacksonville.

"We can't afford to slow down, sit back, or let up, one minute, or one second in the next twenty-four hours... Not now. Not when so much is at stake."

After voting in Chicago tomorrow Mr Obama will make one last campaign appearance in Indiana, ramming home his contention that Mr McCain offers four more years of failed Republican policies when America desperately needs change.

But while the final polls give Mr Obama leads of six, eight and 11 points, Mr McCain is clinging to his hope of a sensational last-minute upset that would confound the commentariat.

"The pundits have written us off just like they've done before and my opponent is measuring the drapes in the White House," the 72-year-old senator told a spirited rally in Tampa, Florida - the first of seven states in which he is touching down today. "The pundits may not know it and the Democrats may not know it, but 'the Mac' is back. We're going to win this election."

After a midnight rally in his home state of Arizona and voting there tomorrow morning, Mr McCain will continue campaigning in Colorado and New Mexico - pressing home his claim that Mr Obama is an untested, inexperienced, tax-and-spend Democrat.

If Mr McCain did win he would be the oldest person ever elected to a first presidential term, while Sarah Palin, his running mate, would be the first female vice-president.

But he must hold every state President Bush won in 2004 or capture a Democratic stronghold like Pennsylvania - a very tall order given that Mr Obama is leading or tied in almost all the swing states. Mr Obama, by contrast, has several likely routes to the 270 electoral college votes required to become America's 44th president.

After a $2 billion, two-year campaign Americans are expected to turn out in record numbers tomorrow - indeed an unprecedented 27 million have already cast early or absentee ballots.

But they will also be electing a US Congress, and with the Republican brand so tarnished Democrats are expected to increase their majorities in both the House of Representatives and the Senate. They key question is whether they can win the nine extra Senate seats they need for the 60 required to defeat Republican filibusters.

Gordon Brown said tomorrow's winner had to offer greater leadership if the world is to recover from its present financial turmoil.

Speaking in Abu Dhabi, the prime minister said: "In the coming weeks and months, the whole world will want to work closely with America on a shared common agenda to bring growth and jobs back to our economies; to give greater stability to our financial system; to defeat protectionism in favour of free trade; and of course to work for a more secure world - and in the Middle East, peace."

But whoever the winner is he will inherit a daunting list of challenges - ending the global economic crisis, fighting wars in Afghanistan and Iraq, and restoring America's standing in the world.

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