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The crowd could sense history in the warm Florida air. The assembled thousands wanted to see the man who stands on the brink of being the first black President of the United States.

Dan Bernard, 49, had brought his three young nephews and nieces. They had driven for hours to attend Barack Obama's rally in the city of Sunrise. "I wanted them to see history. I want them to look back when they are grandparents and be able to say, 'I was there'," Bernard said.

It was a common sentiment. Obama himself shared it. "At this defining moment in history, you can give this country the change we need," he told the cheering throng.

One of the most extraordinary elections ever fought has brought the American people to within two days of casting their vote. They will either elect a young, liberal black senator from Chicago or an old, conservative war hero.

Their choice will affect the entire world.

Obama has brought a touch of the rock star to US politics. He has appeared before crowds of 100,000 or more. He has raised more money than any other presidential candidate in history. His candidacy has more resembled a social movement than a political campaign.

It could end by making a black American the most powerful man in the world and signal a once-in-a-generation change in America.

"He's black and he's got a Middle Eastern-sounding name. Yet the country is positioned to vote for him for President. That's enormous," said Professor Seth Masket, a political scientist at the University of Denver.

But it is not over quite yet. John McCain and the Republican Party remain in the race. They are behind in the polls in the battleground states, but the gap has narrowed recently.

McCain has struck a fiercely populist note and he knows how to fight. All his great triumphs - in war and in politics - have come against the odds. "Nothing is inevitable here. We never quit. We don't hide from history. We make history," he told an enthusiastic crowd in Mentor, Ohio, last week. His beaming grin showed that he believes he can do it.

But it will not be up to him. This race will be decided by tens of millions of Americans at the polls. Only then will the watching world know if the greatest election in recent history has a final twist in its tale.

The election has already been an epic for Obama. His quest for the White House began what seems like an age ago. In February 2007, at the "winter meeting" of the Democratic National Committee in Washington's Hilton Hotel, each Democratic hopeful gave an introductory speech to a crowd of activists. They laid out their stall. Obama's stood out only because it was so bare compared with his ribbon-draped rivals'. There were no placards. No badges or posters. Just a sign-up sheet and a few pens on a desk manned by two young volunteers.

Yet from that humble beginning sprang one of the largest political movements since the Civil Rights era. It has been a triumph of organisation in the technology age. Utilising the internet and driven by tech-savvy young staffers, it has changed the face of American political campaigning. The Obama campaign:* Has 3.1 million financial contributors.

* Has 2.2 million supporters on its Facebook page.

* Is set up in cyberspace and in more than 700 campaign offices in every state, including the ones Obama has no chance of winning.

Through time and money, everyone can still contribute. And they do. Obama has raised US$640 million so far. That has allowed him to outspend and outgun first Hillary Clinton and now McCain. Nothing demonstrated his advantage better than his half-hour national TV advert last week.

No one expected his campaign to change politics this way.

As the first black American to win a major party nomination, Obama was thought likely to face an election dominated by race. Yet his candidacy changed things there, too. He ran an explicitly "post-racial" campaign, heralding a new type of politics. His rallies attract blacks, whites, Hispanics and Asians, reflecting a changing society in which younger generations are less obsessed with race.

Experts predict that will be a Democratic strength in the years to come as minorities make up a larger proportion of America's population. "We are dealing with a country and a generation that feels that diversity is a growing part of who we are," said Stan Greenberg, a Democratic pollster and former member of President Bill Clinton's famed campaign "War Room".

In various forms - such as rumours of him being a Muslim or snide remarks that he is not a "real" American - Obama's opponents have sought to be portray him as the Other. But it hasn't worked. "For the most part, race has been background noise," said Denver University's Masket.

Obama has consciously reached out to the white working class, which is most likely to resist electing a black. He has done it in a conciliatory manner, as a political moderate. Thus Obama - a black liberal - is returning the Democrats to the American South. In Virginia, North Carolina and Florida, he is turning once fiercely red Republican states to shades of Democratic blue. It is yet another unexpected, ironic, turn.

Yet none of it would have been possible without Hillary Clinton. The epic nomination battle that began in Iowa and threatened to continue to the convention floor at Denver forged Obama as a candidate. It meant his skeletons popped out of the cupboard early on, and gave him a ground organisation in each state. The debates sharpened his skills and the media wars honed his team into ruthless professionals.

The nomination fight made Obama as a politician. He stayed cool, calm and collected and so when the greatest challenge of the election - the economic crisis - hit, he was unruffled. As McCain rushed back to Washington, Obama kept his head. As America's economy started to bleed and its financial system collapsed, Obama looked more like the stuff presidents are made of. The polls decisively broke in his direction. McCain has been scrambling to catch up ever since.

McCain hit Ohio last week in a bus blitz. With him was the man who has become the last-ditch "working man" symbol of the Republican campaign: Joe Wurzelbacher - Joe the Plumber.

In Mentor, Ohio, a small working-class suburb of Cleveland, Wurzelbacher got a hero's welcome from several thousand people. He told them he was voting for a "real American" in the shape of McCain.

McCain was gleeful and strident:"I have been in a lot of campaignsand I have seen momentum. I canfeel the momentum in this room tonight. I can feel it. I can feel it."

He will need it. Obama has bitten deep into Republican territory, appealing to white-working class voters, rural voters and the "exurbs". Only a last-minute wave of support, or some unforeseen flaw in the opinion polls, can propel McCain over the finish line in first place. His support is vocal and numerous, but feels out of touch with changing American concerns.

His campaign has portrayed Obama as a socialist, someone who will raise taxes. Or a dangerous radical who "pals around" with terrorists. It has worked for the party's core support. "I don't like Obama. I don't like marxism. It is not American," said Mark Kopan, an IT consultant who wore a T-shirt opposing anti-illegal immigration.

But McCain's real problem has not been Obama. It has been the past eight years of Republican rule and President George W. Bush. In poll after poll, it has been obvious that Americans everywhere desperately want a change in direction. Now the cracks are starting to show in the once-formidable Republican machine that as recently as 2005 was plotting the creation of a "permanent majority" in US politics.

The conservative right has already planned a meeting this week in rural Virginia to discuss how the party should move forward after election day. "The next two years, maybe longer, will be a time of internal conflict and soul-searching and messiness," said Larry Haas, a political commentator and former aide in the Clinton White House.

On the campaign trail last week, the two sides felt starkly different. Even the town names suggested a fight between experience and optimism: Mentor versus Sunrise.

The queues for Obama's event began hours before it opened and stretched for kilometres. There was a carnival atmosphere inside a vast stadium. For McCain, it was a school gym and the queue never left the car park. Inside, it was patriotic shouts of "USA! USA!" McCain launched into a scathing attack, playing on the familiar themes of cutting taxes, supporting the military and boosting Joe the Plumber's working-class authenticity. Obama's rhetoric soared amid talk of unity and change. His running mate, Senator Joe Biden, mentioned a pantheon of US political Gods: Thomas Jefferson, Abraham Lincoln, Franklin Roosevelt and John F. Kennedy.

But hubris is dangerous. The final words do not belong to any politician. They belong to voters. Their collective decision could put a black man in the White House, or it could reject him for an ageing warrior who found his political soul-mates in the form of an Ohio plumber and a Hockey Mom. America is at the crossroads.

- OBSERVER