Inviting me into the living room of his small wooden bungalow, Leslie Johns declaims like a fiery Baptist minister - but with considerably more fiery language. "Look at Bush with his slick ass, helping out all those Wall Street bankers," he preaches - to the converted, as far as he is concerned. "You bet I'm voting Obama, but not because he's black. I'm voting because he's not Bush." He shifts back to conversational register. "It's wonderful you're here, by the way."

For all his passion, 2008 would be the first year that Mr Johns has voted. On just my second day volunteering with the Colorado Obama campaign, it is my job to make sure he fulfills his promise.

Now that the time for voter registration has passed, the objective of thousands of eager Obamaites across the country is to make sure that those who are able to vote (and, of course, likely to vote Democrat), vote early, vote by post or - at the very least - know where to vote come November 4. Their worry is that Obama's narrow poll lead in states like Colorado will be negated by new voters - invariably left-leaning - failing to follow procedures: not including photocopied IDs with their postal ballot, not understanding English, or simply not knowing where to turn up.

Mr Johns' small Denver suburb is a broad sprawl of single-storey homes - demarked by a wide concrete overpass to the east and light industry to the south. A week before Halloween, pumpkins and witches share gardens with tattered Stars and Stripes, as well as, in Latino homes, the occasional Virgin Mary. Blue collar, high unemployment, mainly ethnic minority: for Democrats, this is prime Get Out The Vote territory.

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As I work through even numbers - knocking on doors, answering questions - a fellow volunteer, Amelia Jenkins, covers the odds. Ms Jenkins has a full-time job in Washington DC but has taken three weeks off work, hired a dogsitter and - along with scores of other volunteers from safe Democrat states - come to help traditionally-Republican Colorado turn blue. This is their Spanish Civil War - and in the final week of the election, the Democrat machine is recruiting in a way that has perhaps not been seen since the 1972 McGovern campaign.

Some of our targeted homeowners are suspicious. Some refuse to come to the door. Others hide behind twitched curtains until we leave. We are like political Jehovah's Witnesses, but we are unrepentant. And, were we to falter, back at West Denver's Obama HQ hand-painted signs urge us to keep up the canvassing - or "cutting the turf", as they call it - to help save America.

As afternoon becomes evening, Get Out The Vote switches to remote mode: telephones manned by rotating groups of volunteers call page after page of voters, selected by computer.

Most of my calls go to answer machine. I invite one women to a rally, only for her to point out that - age 91 - rallying isn't really her thing. Another, a man aged 83, interrupts me mid-pitch. "Are you Democrat? I'm already voting Democrat, so stop calling me already," he says before hanging up. A colleague explains that if people have received postal ballots but not yet voted they can be called three or four times a week.

Taking a break, talk turns to tales of canvassing. "A friend of mine told me he was out on the trail, and he got invited in by a Republican who gave him hot chocolate," someone says. "I said to him: "You know what they put in Republican hot chocolate? The tears of starving children'".

"Republicans don't invite you in," someone else responds sceptically. On the wall behind her a seraphic, technicolour Obama gazes into the middle distance. The caption below contains just one word: Hope.

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