This long-red suburban Denver county gave President Obama a 12-point win in 2008 after going for George W. Bush by four points in 2004 — a 16-point swing in four years. It also accounts for about 10 percent of the statewide vote. The winner here is likely to win statewide.
Obama is going to win this county, as have all recent Democratic presidential candidates. But the question is by how much. Des Moines-based Polk accounts for about 14 percent of the statewide vote and gave Obama a 57 percent to 42 percent win in 2008. Romney needs to keep Obama in the low 50s, where Democratic candidates were in 2000 and 2004.
Obama will rack up big margins in Dane (Madison) and Milwaukee counties, while Romney will score huge wins in suburban Waukesha and Washington counties. Meanwhile, Appleton-based Outagamie is as swingy as they come. It went for Bush in 2004 by nine points and for Obama by 12 — a 21-point swing.
This suburban Philadelphia county went for Bush by four points in 2004 and then for Obama by nine points in 2008. It's also about 4 percent of the statewide vote. Much in Pennsylvania depends on how many votes Obama can wrack up in Philadelphia, but he wouldn't have won the state in 2008 without the margins he took in the suburbs too. If Romney somehow pulls the upset, it will be because he did well in counties like Chester.
Hillsborough County (Fla.)
The host county for the Republican National Convention is home to Tampa and the most valuable voters — arguably — in the country. It's vote in 2008 mirrored the statewide vote (51-48 for Obama) and closely reflected the statewide vote in 2004 as well, with Bush winning 52 percent statewide and 53 percent in Hillsborough. This is really the heart of the I-4 Corridor.
This suburban Richmond district went for Bush by eight points in 2004 and then for Obama by a whopping 12 points in 2008. That 20-point swing is one of the biggest in the country. Henrico could be a good indicator of where voters in the middle are going.
Cincinnati-based Hamilton County is split between urban liberals/African Americans and heavily conservative suburbs, and the side that wins this county will likely win statewide. The county went for Bush by five points in 2004 and for Obama by five points in 2008. It also accounts for about one in every 13 voters in the state, so the swings here matter.