The line snaked down the middle of Columbus for more than a mile, old white ladies dancing to Aretha Franklin, young black men hugging them, toddlers clutching “Yes We Can!” banners: a big, feel-good, central Ohio Barack Obama love-in, hiding bags of last-minute nerves.

Many had walked for miles to attend one of the final rallies of the Democratic candidate in the heart of this crucial battleground, clad in a dazzling array of Obama clothing that could fill a fat catalogue: T-shirts proclaiming “Hope!” and “Change!”, “Obama ’08: Mission Impossible”, “Together We Stand”, “Obama, the Next President”, “I Love Obama” and simply: “Yes”.

By the time that Mr Obama walked down the Ohio statehouse steps at 1.30pm, clutching the hands of his daughters Sasha and Malia, the huge crowd was roaring and whistling and whooping, chanting “OBAMA” and “Yes We Can!” A grey-haired octogenarian jigged to Bruce Springsteen’s The Rising as it thumped from giant loudspeakers. “I am overwhelmed by this crowd,” Mr Obama declared. “It’s unbelievable. Ohio, I have just two words for you: two days!”

Yet beneath the energy and party atmosphere – with a crowd of 60,000 it was the biggest political rally in the history of Columbus – and the heady excitement that after this marathon campaign they had at last reached the cusp of history, many of these Ohioans were suffering a new mental condition on the eve of Election Day. It could be called “Victory Will Still Be Snatched From Us Compulsive Disorder”.

“I am so afraid some ghastly trick will be played again and we’ll wake up on Wednesday morning and we’ll be where we were in the last two elections,” said Stephanie Harper, 32, as she walked towards the rally with thousands of others. “My doctor says she is treating lots of Democrats for anxiety and depression, because of their obsession with this election and their fears that Obama will lose.”

Like Florida Democrats, who will never be dissuaded that the 2000 race was not stolen from them, their counterparts in Ohio still believe, without compelling evidence, that John Kerry was robbed of the presidency in 2004 because of Republican dirty tricks on voting day here. If the Democratic nominee had won 60,000 more votes in the Buckeye State four years ago he would be in the White House today.

Alec Clairmont, 23, described himself as extremely nervous, and was muttering darkly about a documentary he had seen the night before alleging that “people can programme voting machines so that they can send votes to the other side”. He added: “The polls look good, but I don’t know what will happen on election day.”

Wearing a shirt declaring “Another Old White Woman for Obama”, Annie Horner, 63, said that anxiety levels were intense, but she was telling her friends who were worried “not to put all that negative energy out there”. Mr Obama, she said over the strains of U2’s Beautiful Day, would be propelled to the White House on a wave of “positive energy”.

Mr Obama and his aides are taking a somewhat less holistic approach in these last hours. They realise that the road to the White House runs through Ohio and its 20 electoral college votes, and have put in place an 11th-hour get-out-the-vote operation that is brutal in its scale and intensity.

This election has been going on so long, and living rooms have been filled with so many television pundits poring over electoral maps, that children born when Mr Obama declared his candidacy can probably recite today the reasons why Ohio is so important.

No Republican has ever won the White House without it. From 1904 to 2004 the Ohio victor won the presidency 24 of 26 times. Only two Democrats – Franklin D. Roosevelt in 1944 and John F. Kennedy in 1960 – won the presidency without carrying Ohio. Four years ago President Bush beat Mr Kerry here by two points, delivering his reelection.

The visit by Mr Obama yesterday, the first of the final six rallies of his two-year White House quest, was his 33rd visit to Ohio since September 5; Mr McCain has made 28 during the same period. It has been the most visited state by the candidates, and if the Republican loses here tomorrow his presidential hopes will almost certainly be ended.

Aides to both candidates agreed that Ohio remained extremely close. After his rally in Columbus Mr Obama was due to hold two more events here, including an appearance with Springsteen in Cleveland.

During his speech Mr Obama urged Ohioans to get themselves, and their friends, to the polls. “Columbus, don’t believe for a second that this election is over,” he told them.

What to watch for and when to watch it

What states should I look at? The US election 2008 boils down to these states: Florida, Ohio, Virginia, Colorado, Pennsylvania and Nevada – although keep tabs on North Carolina, New Hampshire and Iowa

When do the polls close? Midnight GMT in Virginia, Florida and New Hampshire, and 30 minutes later in Ohio and North Carolina. In Pennsylvania they close at 1am, Colorado 2am, in Nevada and Iowa 3am. Alaska is at 5am

So when should I get excited? This is risky territory, but if Obama looks like he has won the early states – Florida and Virginia – we should have a good indication of this before 2am. Obama-maniacs might think about the champagne at this point. McCainiacs need him to hold on to Florida to stay competitive – and if the Republican wins in Ohio as well the night becomes more interesting

Why might I need to stay awake? If most – or even some – of these states are going to Obama it is a Democratic win (probably). If McCain scores some early upsets and the polls have all been wrong, then look for the exit polls in places such as Colorado and Nevada

Who is covering it? A cast of thousands – David Dimbleby on BBC One from 11.20pm; Alastair Stewart on ITV1 from 11.45pm; Jeremy Thompson leads Sky News from 11pm; plus everyone from Al-Jazeera to Fox.

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