No Republican candidate, from Abraham Lincoln in 1860 to George Bush in 2000, has won a United States presidential election without winning Ohio.
It is widely recognised that the Democrat candidate, Mr John Kerry, will not win without carrying the state - Mr Bill Clinton was victorious there in 1992 and 1996, while Mr Al Gore lost by a narrow 3.6 per cent four years ago. So far this year Mr Bush has visited the state six times and Mr John Kerry 12 times. Both of them campaigned there this week, making the presence of US troops around the world a major election theme.
Ohio is one of the proverbial swing states because it is a microcosm of the US electorate in so many ways and has 20 electoral college seats. It was the 17th state to join the Union in 1803 and by 1850 was the third most populous one. Early industrialisation which has continued since then attracted German, Swiss, Irish and Welsh immigrants and large numbers of black workers. The only prominent ethnic group under-represented there are the Hispanics. Ohio's Midwest location, bounded on the north by Michigan and Lake Erie, on the east by Pennsylvania and West Virginia and on the west by Indiana make it geographically representative of a wide swath of states. This is mirrored by the mix of agricultural and industrial employment, with a cattle and corn belt sympathetic to Republicans and the north-east industrial area to the Democrats. Religious fundamentalists favour Mr Bush, while Mr Kerry has strong urban support.
Politically Ohio is dominated by Republicans, who control the governorship, the two Senate seats and the state legislature - largely because they have recently had a superior organisation there. But the latest polls show the parties with virtually equal support among the 60 per cent or so who intend to vote. Recent job losses and the drift to less well-paid service employment have made the economy a strong campaign issue for the Democrats.
Mr Bush has sought to rally traditional support by patriotic rhetoric in support of the war in Iraq, mocking Mr Kerry's reference to a more sensitive foreign policy ahead of next week's Republican convention. For the first time since 1972 foreign affairs, national security and terrorism issues are found by the Pew Research Centre poll published this week to be greater concerns than economic affairs. This could go either way for the Bush administration, in Ohio and other swing states such as Pennsylvania, Florida and Illinois. A great deal will depend on what happens in Iraq and on which candidate voters feel can best guarantee their security.