The Swing Counties, and How They Swung

· PRINCE WILLIAM COUNTY: Much like Loudoun, Prince William was once solidly Republican. But it also went for Kaine and Webb, albeit narrowly. Democratic political strategists say Prince William is one of the most difficult Virginia counties to predict. Over the past year, the GOP-controlled Board of County Supervisors has enacted some of the most stringent laws aimed at illegal immigrants in the country.

Last year, county voters gave Democratic candidates cause for worry during state legislative campaigns because polls showed that Prince William was the only place in Northern Virginia where voters weren't responding to the Democratic message.

In recent presidential contests, Prince William has given Democratic candidates slightly better numbers than in Loudoun. Bush won Prince William with 53 percent of the vote in 2000 and 2004.

Obama should start with a solid base because Prince William is about 20 percent black, but McCain could do well among the county's large numbers of active and retired military personnel.

Result: Obama won Prince William County by 25,814 votes. Obama received 57 percent vs. McCain's 41 percent.

· RAPPAHANNOCK COUNTY: Rappahannock, in the foothills of the Blue Ridge Mountains, has a population of about 7,200. But it sometimes stands out on election night electoral maps because it is a Democratic dot surrounded by solidly Republican counties. Bush won Rappahannock by about 350 votes in his two races. In 2005, Kaine won it by 114 votes. A year later, Webb won it by 148 votes.

Result: McCain won Rappahannock County by 122 votes. McCain received 51 percent vs. Obama's 48 percent.

· CAROLINE COUNTY: Caroline, with about 27,000 people, is just south of Fredericksburg. It often sways between the two parties. Former vice president Al Gore (D) carried it by 441 votes during his presidential bid in 2000, but Bush won it by 121 votes in 2004. A year later, Kaine carried it with 54 percent of the vote; in 2006, Webb won it by 191 votes. Turnout among African Americans, who make up 29 percent of the county's population, is key to Democratic prospects.

Result: Obama won Caroline County by 1,546 votes. Obama received 55 percent vs. McCain's 43 percent.

· HENRICO COUNTY: Richmond's conservative suburbs have rarely flinched from their Republican leanings since the early 1970s. But Democrats are optimistic about Obama's chances this year in Henrico, which surrounds Richmond.