Now, to their amazement, Arizona is within reach. The latest polls show Senator McCain, the Republican presidential candidate, is leading by less than 4 percentage points in the state he has represented for 26 years.

Enthusiasm for Barack Obama's message of hope, and anger towards the President, George Bush, have helped the Democrats in this staunchly Republican state mobilise waves of volunteers and muster donations.

At a makeshift headquarters in Phoenix, handwritten signs across the wall implore "Let's Turn Arizona Blue" and "Yes. We Can!". Others, mocking their own campaign's slogans, declare "Dogs for Obama" and "Cheese you can believe in".

The volunteers are young; the mood upbeat. There are bowls of fruit and noodle soup (volunteers at the nearby Republican headquarters graze on glazed doughnuts and blueberry muffins).

It had seemed a formality that Arizona would go to its senior senator, who had been leading with a consistent margin of more than 10 points. The main newspaper, The Arizona Republic , handed Senator McCain its inevitable endorsement, saying: "As much as an electorate can, we know this man."

For the past 60 years, the Republican candidate has won every election except 1996 - when the independent, Ross Perot, split the conservative vote.

Not surprisingly, most of the Democratic campaigning had avoided the presidential race and concentrated on so-called down-ballot contests, such as the battle to replace Joe Arpaio, a Republican who calls himself "America's toughest sheriff" and is notorious for humiliating prisoners by forcing them to wear pink underwear and eat green-dyed food.

Volunteers who wanted to campaign for Senator Obama were invited to call voters in neighbouring states or sign up for bus trips to New Mexico, which George Bush narrowly snatched from the Democrats in 2004.

"This is McCain's home town," an Arizona Democrat campaign official, Joanne Peters, told the Herald . "We have all been assuming it will be lost."

But in recent days the polls have begun to turn. The website RealClearPolitics has switched the state's status to "toss-up" after Senator McCain's lead shrunk to less than four points. In turn, Senator Obama launched his first television campaign in the state - and the volunteers are starting to make local calls.

"[It's] a very, very close race," said Senator Obama's campaign manager, David Plouffe.

Unlike the Obamamania that has helped to mobilise Democrats, Arizona's Republicans - who tend to be on the party's right - have found it difficult to muster enthusiasm for their favourite son.

The mood in the headquarters outside Senator McCain's office is quieter and less frenetic.

Many Republicans here were outraged by Senator McCain's earlier support for immigration reforms. Sheriff Arpaio, who in the past two years has turned his attention from prisoners to cracking down on illegal immigrants, pointedly endorsed Mitt Romney in the primaries.

"Senator McCain is a little bit different in his ideas," said his former chief of staff Paul Hickman. "He has always believed that we needed to expand the party. Even if John McCain wins … the party will need to rebuild itself."