"Curious about what?" I ask. "I'll talk to you later," said Cleo Toris (run the two names together quickly) to the laughter of the mainly gay and lesbian crowd at the Black Tie Affair in Springfield, Missouri.

With a proud crop of manly chest hair poking out of her pink harem outfit, Cleo Toris is no regular drag queen.

But then this is just the biannual turn of raucous stand-up she does for charity.

The rest of the year she is Mark Gideon, a 47-year-old education administrator.

Mr Gideon is the only graduate of the Evangel University, a devout Christian college situated in Springfield (population 151,580), to be crowned Ms Missouri by the International Gay Rodeo Association. "I got wonderful training at Evangel," he says. "But I was shocked the first time I went into a gay bar and found half my Bible class was in there." There are around 71 Springfields (not including the one the Simpsons live in) dotted around 36 states and territories of America, from the Virgin Islands of the Caribbean to Vermont in New England. Georgia alone has nine; Virginia has eight.

But the Springfield in Missouri is special. It is the home town of fundamentalist attorney general John Ashcroft, a man so religious he holds daily Bible study classes in his office and so prudish he ordered the naked breast of a statue in the justice department be covered. It is also the headquarters of the Assemblies of God Church - Mr Ashcroft's church - whose base is locally referred to as the Blue Vatican.

But it is also home to a thriving, resilient and somewhat embattled, lesbian and gay community, with five gay bars, a gay theatre, and a community centre. Up in the surrounding Ozark mountains are several lesbian collectives that nestle alongside hippy communes and militia camps, said to "get on because they leave each other alone". The Black Tie Affair raised money for three lesbian and gay organisations and an Aids project. "It's changed a lot since I came out in the 70s," says Mr Gideon. "Back then it was just bars and the park. Now we're better organised."

A year ago the climate looked encouraging. The supreme court had recently repealed the sodomy laws, finally making gay lifestyles legal. A few months later Massachusetts became the first state to make same sex marriage legal. Then came the backlash. Missouri passed an amendment to its constitution effectively outlawing gay marriage by a huge margin of 71% to 29%.

President George Bush is vowing to amend the federal constitution to do the same if elected; his challenger, John Kerry is opposed to gay marriage but argues it should be left to the states. In this election year gays and lesbians in general and gay marriage in particular have become a central issue. It is the means by which Republicans hope to mobilise their fundamentalist base on election day and the subject Democrats wish would just go away.

In 11 states, including the battlegrounds of Arkansas, Michigan, Ohio and Oregon, the presidential election is twinned with a referendum on amending the constitution to outlaw gay marriage. And polls suggest all of them are likely to pass. "It's just about the perfect wedge issue," says Jeff Wunrow, executive director of the Missouri-based lesbian and gay rights organisation, Promo. "It galvanises Republicans and splits some of the Democratic base."

The day after Missouri's constitutional amendment passed, Melissa Marles was wary when she went into work, where she is "out" to just a few people. "I didn't know what I would hear and I knew I was going to have to stifle my feelings. I thought 'This many people thought it was okay to do that'. I was a little uncomfortable."

When Stephen Adams, a doctor in Springfield, heard the results of the constitutional amendment in Missouri, he was "ready to move". But his partner, Randy Doennig, took heart from the way the gay community stood up to the attack.

"We went door to door campaigning," says Mr Doennig, president of Promo. "That's the first time we had gone door to door about anything; the first time we were engaged on a local level and we had to talk about gay marriage. They don't take us seriously because we haven't asked them to take us seriously."

Mr Doennig points out that the vote in the areas where they canvassed was much closer. "Our neighbours and people that we talked to voted for us," he says. "If we all run away and go somewhere else then who changes this place? It just needs a shove."

When you move from Iowa to Missouri you cross the Mason-Dixon line into hybridity; a racial, cultural and historical blur that blends the Midwest with the upper South. This is Mark Twain country - a former slave-owning state that the slave-owners failed to win over during the civil war. The deeper you journey into it the more languorous the drawl and the more plentiful the churches.

Long before you get to Springfield, Missouri is pronounced Missurah. In 2000 Mr Bush won Missouri by 50% to 47% and this year it was slated as one of the original 17 key battleground states.

But as the race draws to a close the campaigns are cutting their losses in areas they think they cannot win and concentrating their resources in those where they have more chance. Mr Bush, for example, has all but given up on Michigan; and Mr Kerry has given up in Missouri, where Republicans now hold a six-point lead.

Mr Kerry's message about jobs and healthcare and Iraq could not penetrate the touch button "value" issues of abortion, guns and gays in a state where 36% of voters are evangelical Christians.

"I think it's a mistake," says Dave Robertson, a political scientist at the University of Missouri in St Louis. "I think the election will be close and whoever loses will probably have lost Missouri and regret not doing more to get it."

Back in Springfield, Phil from Chicago heads to the gay bars with an armful of Kerry stickers, determined not to abandon the state just yet. "People are so short-sighted," he says. "They can vote against abortion but there'll still be abortions. They can vote against gays but there'll still be gays."

At the Black Tie Affair, a photographic exhibition illustrates that there has always been a gay community in Springfield, even if the rest of the community was not aware of it. A grainy picture of four men dancing next to an old radio was submitted by a woman who said she knew her "uncle was a little different". Then there is a shot of Rick in his army uniform during the 70s with the caption: "They didn't ask and he didn't tell." And there is a younger Cleo Toris, when she sang with the Mexican Villa Girls.

But the accompanying text shows that when they have put their heads above the parapet there have been mixed results.

In 1989, when Springfield's South West Missouri University put on The Normal Heart, a gay-themed play about Aids by Larry Kramer, one of the men who promoted it had his house burned down. Now the Vandivort theatre in the centre of town is showing Bent, a play about Nazi persecution of homosexuals.

Springfield has no gay pride parade because the town has not outlawed discrimination in the workplace for lesbian and gay men, says Mr Doennig. "A lot of people are worried about being fired."

But last year the town did see an eight-fold increase in membership to Promo. "We've only been tolerated because we've remained silent," agrees Mr Adams. "But we just can't be silent anymore."