We’re all familiar with a certain political geography. Democrats win the cities, Republicans win the rural areas, and the battlegrounds are in the suburbs. In general, Democrats win the denser inner-ring suburbs where there are lots of professionals — doctors, lawyers, teachers. Republicans win the sprawling outer-ring suburbs, where there are lots of office parks and midlevel corporate managers.

Northern Virginia has always embodied this familiar suburban divide. Democrats have done well in inner-ring towns like Arlington. Republicans have done well in outer-ring boomburbs like Loudon County. In 2004, for example, George W. Bush trounced John Kerry in Loudoun County by 55.7 percent to 43.6 percent.