Ohio is where the warring halves of America meet. This midwestern state, mixing rural farmland, small towns and decaying industrial cities, is the ground zero of the bitter and protracted 2012 election that on Tuesday will decide who wins the White House.

It is where blue state Americans, who back Barack Obama to win a second term, battle over turf with red state Americans who desperately want Republican challenger Mitt Romney to bring the right back to power.

Ohio has voted for the winning candidate in very election bar one since 1944 (in 1960, it went for Nixon over Kennedy). No Republican has ever won the White House without taking Ohio. If Obama can stop Romney here, he is likely to emerge the victor. But if Romney can take the state it will signify a ground shift: one that will reduce Obama to a humbled, one-term president. Both sides know this.

In the small town of Celina in western Ohio last week, the state's lieutenant-governor, Mary Taylor, was acting as a warm-up act for Romney and his running mate, Wisconsin congressman Paul Ryan. In a high school sports hall she warned a packed crowd: "The world is watching Ohio." A day later, on the other side of the state – literally and metaphorically – former president Bill Clinton was oozing Arkansas charm in the "rust belt" city of Youngstown. "Ohio is an old-school kind of state, and I mean that in the best possible sense," Clinton drawled. "Obama had your back when you were against the wall, and you will have his back now."

This, after months of brutal campaigning, is where it ends. All the heat and fury of almost two years of rallies and speeches, all the relentless attack ads, all the politicking and horse-trading, comes to a head this week.

Across America there are only a nine states where votes matter. Giant states such as Texas and California are already in the bag for, respectively, Romney and Obama. Instead, these few swing states – from Colorado in the west to Florida in the south and tiny New Hampshire in New England – are the battleground on which the election has been fought. The fight there is poised on a knife edge. Romney's surge after the first presidential debate has abated and left the national polls largely tied. In the swing states – and, crucially, in Ohio – Obama holds a slim but steady lead. That means, as the election goes down to the wire, it is Obama who many believe has his nose just ahead.

But the last week has seen a frantic final push. Across the swing states tens of thousands of party volunteers have gone door to door. The "get out the vote" plans for election day are being rehearsed and fine-tuned. Airwaves in the swing states are so saturated with political ads that in some areas there is no ad space left to buy. Even superstorm Sandy – which devastated the north-east – saw the campaign suspended for only a couple of days before combat resumed. By the time people vote on Tuesday a staggering $2.5bn will have been spent on the election – the most expensive in history.

Yet in Ohio, despite the intense effort, two different realities stubbornly persist. John DeCaussim, a 56-year-old Youngstown mechanic, said he could not understand how anyone could vote for Romney. "I have no idea why this election is close," he said. "It shouldn't be." Meanwhile, in Celina sales manager Jim McGee, 62, believed Obama was a threat to the country's existence. "He's been a disaster. In my lifetime I have never seen things fall apart so far," he said.

For Republicans the importance of winning Ohio is maths and history. Every Republican president has had the state on his side. And almost every plan that party strategists have devised to grab the White House for Romney includes Ohio in the win column. As a result, the Romney campaign has been virtually camped in the state. Romney has visited almost 50 times this year alone. Ryan too has been a virtual ever-present.

The state has seen a remarkable transformation of the Romney message over the last week. He has sought to shed his conservative image and long career in high finance and turn into an economic populist, emoting about tough economic times and bewailing the plight of the poor. In Findlay, Ohio, a small college town with a dilapidated Main Street, Romney was in full flow. He told stories of single mothers, low wages and parents making sacrifices so they could buy birthday presents for their children. For Romney, a millionaire many times over who has repeatedly extolled the virtues of high capitalism, it was a jarring performance. "There has been a middle-class squeeze in this country," he said.

Romney even started to sound like Obama circa 2008. He has adopted the "change" slogan as his own, portraying himself as an enemy of the status quo. "I happen to think that the American people understand that we need dramatic and real change," he said. Ignoring the last three years of bitter politics and a Tea Party-dominated Republican party, he claimed to be a centrist, keen to reach out a Republican hand to Democrats, even though it is the same hand that has been rejecting Obama for his entire first term.

But Romney as populist fist-pumper was as nothing compared to the musical act in Findlay. Before the teetotal, Mormon former Massachusetts governor took the stage, country music stars John Rich and Cowboy Troy, a black rapper, gave a lyrical performance, singing I Play Chicken with the Train. Rich suggested the crowd treat polling day like a drunken football game day party. "I would make a tailgate party and go to vote for Mitt Romney. Put that man in the White House, can you hear? Oh yeah," Rich said. "Put some beer in the cooler in the truck!"

But if such contradictory images were a sign of a notoriously fluid Romney, keen to find any message that sells in Ohio, there have also been signs in recent weeks of the Republican party's knife-sharp edge. Across America mysterious anonymous "robo-texts" slamming Obama have been buzzing millions of people's mobile phones. Billboards appeared in Ohio, and other swing states, apparently targeting poor and minority neighbourhoods with warnings of the threat of prison for voter fraud.

On the airwaves the ads have got more extreme. A Romney ad claiming Jeep production was being moved to China was condemned as an outright lie by Jeep's own parent company, Chrysler. Another ad, running in Florida, linked Obama to Cuba's Fidel Castro and Venezuelan president Hugo Chávez. Neither is virulent dislike for Obama hard to find, often tinged with a sense that the president is not really American. "I want to support Romney the good old-fashioned American way," said construction worker Kevin Williams, 48, in Celina. "I don't like socialism and Obama supports that."

There is little doubt that Republicans are highly motivated. Maggie Niswaner is 73 but reckons she has walked more than 20 miles in the last week, knocking on doors and delivering pamphlets as a volunteer for Romney in Findlay. "I am a good American," she said when asked for a reason why she was putting in such efforts to defeat Obama.

The doom and gloom pumped out by the Romney campaign has worked, too. Though there is little doubt the economy is stuttering in its recovery, and unemployment remains high, but has been on a downward trend. But that is taboo on the Republican campaign trail. "We have a jobs crisis in America," said Paul Ryan in Celina, pointing out that 23 million Americans were struggling to find enough work.

But Ryan is right about one thing. It is a favourite part of the firebrand conservative's performance to read out a quote at the beginning of his stump speech. It goes: "If you do not have fresh ideas, use stealth tactics to scare voters. If you do not have a record to run on, paint your opponent as someone that people should run from." Ryan then asks his audience who said that and delightedly gives the answer. "That's what Barack Obama said when he was running for president four years ago. Now when you switch on the TV that is exactly what he has become," Ryan said in Findlay.

There is much truth in the claim. Obama's re-election campaign, led by the hardnosed political operative David Axelrod, has been relentlessly negative. It has been a brutally sustained assault on Romney's image. One controversial – and widely debunked – attack ad all but accused Romney of killing a man's wife after she lost healthcare benefits. Obama has raised and spent hundreds of millions of dollars on negative advertising and Bill Clinton and vice-president Joe Biden have become even punchier as the campaign has drawn to a close.

In Youngstown, Clinton mocked Romney's flexibility of ideas, perhaps forgetting his own notorious "triangulation" of policy. "Romney ties himself in more knots than a boy scout does at a knot-tying contest," Clinton quipped. Biden followed suit. "This guy pirouettes more than a ballerina," he said, bringing a cry of "Romney is a liar!" from the audience.

It is not a pretty end to Obama's campaign. And it is a long way from "hope and change". Though few ever expected Obama to fulfil the wild expectations of his historic 2008 election win, his first term has ended with a disappointed liberal base dismayed by broken promises on union rights and closing Guantánamo Bay and by a resounding defeat in the 2010 midterm elections. The result has been an Obama effort that has only hesitantly defended its main policy achievement of healthcare reform and has focused on attacking Republicans, rather than laying out any bold agenda.

Yet, for many on the blue state side of Ohio's divide, that is more than enough. On the streets of Akron, a city at the heart of the north-eastern rust belt, student Cara Chappell remained loyal. "When Obama came in it was already all messed up," she said. "The next four years he will be able to get things right. He had to save the economy first."

She cannot conceive of a Romney victory, even as she admits that her mother – who boasts a technology degree – cannot find work and might leave the state. "If Romney wins, I will probably be speechless for the first time in my whole life," she said.

So will Axelrod. Buoyed by polls showing that Obama is holding on to a slim lead in Ohio, his political guru was in a bullish mood. "I don't want to be ambiguous at all: we are winning this race," he said.

Of course, both sides cannot be right. Unless the election is so tight that it ends up in court decisions and recounts, either blue state America or red state America will triumph. But the warring sides agree on one thing. As Ryan looked out over an enthusiastic crowd of Republican true believers in Celina, he told them: "Ohio, you get to decide." That decision – whatever it is – will affect the whole world.

© 2012 Guardian News