Why the Buckeye State holds the key to the White House

The small shindig to celebrate the opening of an Obama for President office in a strip mall near the centre of Strongsville in Cleveland, Ohio, is a relaxed affair. Volunteers swap campaign gossip and pick at devilled eggs and cold pizza. Topic A: the drubbing, as they saw it, of Mitt Romney at the debate the night before.

Yet this evening's social is merely a pause in a ferocious war the outcome of which is still in the balance. True, the Barack comeback at the Hofstra University debate on Tuesday may have an impact on the race, yet the fate of his re-election campaign will also turn on the efforts of these 20-odd volunteers and others like them.

"This is push time," Carolyn Reed, 63, said in a tone of urgency and a little glee. Wearing a "Made in the USA" button with an image of Mr Obama's sometimes contested birth certificate, she adds quickly: "And we really have to push a lot!"

Of the 10 or so swing states that will decide this election, none matters more than this one. It is why Mr Obama jetted to Ohio after Hofstra on Wednesday, making his 16th visit to the Buckeye State as president and why Mr Romney and running mate Paul Ryan have recently made Ohio a virtual home away from home.

The reasons are stark. As Mr Obama has seen his edge in the polls evaporate since the first debate in Denver, Ohio has become his final firewall against defeat. By turn for Mr Romney the state is a must-win, pure and simple, not just because it will deliver a large trove of 18 Electoral College votes on 6 November – it takes 270 of those votes to win the White House – but also because of the evidence of history. No Republican has become president without winning Ohio. The last Democrat to take the White House without Ohio in his column was John F Kennedy in 1960. Add to that the fact that Ohio is in many ways a microcosm of this country. It has multiple large urban areas that continue to favour Democrats. Many also have large black constituencies, although missing from Ohio is a significant Latino presence. The Republicans have redoubts, too, in the rural Appalachian country in the state's east and south and in recently grown suburbs like Strongsville.

"Taken together, it is a fairly close mirror of the country, demographically, economically, socially," agrees Gene Beaupre, a professor of political science at Xavier University in Cincinnati, in the state's western edge. "I think that's one reason it has accumulated a history of being important." There are large universities, coal mining regions, farming communities and industrial areas that have suffered severely from the loss of manufacturing.

Both parties know that winning or losing will depend on their ground games in the swing states. That means having the volunteers like Ms Reed and giving them the tools and the data to knock on the right doors and canvass the right homes. The evidence is that Team Obama is better at this – there are now nearly one hundred field offices like this working the grassroots for Mr Obama in Ohio, for instance, versus less than 40 for the Republican ticket.

While ahead of Denver, Mr Obama seemed almost to have Ohio in the bag, today it looks entirely more dicey. Two polls released last night, one by Rasmussen and another by SurveyUSA, gave the president leads of only one and three points respectively, by no means safe margins. And each side has been talking up their chances of taking the state, notably to reporters crammed into the "spin room" at Hofstra straight after Tuesday's debate.

David Plouffe, the top Obama strategist, raised eyebrows when he named Ohio, Nevada, Iowa and New Hampshire as the four bastions of support that would ensure his candidate's re-election. (The comment elicited headlines that the Obama campaign was giving up on Virginia and Florida, which it hastily denied.) If they are indeed confident of Ohio, one reason may be the trends in what has already been heavy voting in the state. As of the end of last week, one in five Ohioans had voted and Obama was winning those early voters by 63-37 percentage points.