The White House race may come down to an even narrower slice of the electorate than simply the nine most competitive states.
An Associated Press analysis suggests that the race probably will be decided by what happens in the 106 counties that Republican George W. Bush won in 2004 and that voted for Democrat Barack Obama in 2008.
In Virginia, it may come down to voters who live amid the affluent subdivisions and Civil War battlegrounds of Loudoun County.
Voters in the Hamilton County suburbs around the humming riverside economic engine of Cincinnati may tip Ohio.
Florida likely will go to the winner in Hillsborough County, where the urban seaport town of Tampa bleeds into communities of Spanish-speaking voters and retired Midwesterners.