VA is not only very black, but also has seen its northern counties of the D.C. area invaded by leftist bureaucrats on the government dole and others who fled the very Blue state of Maryland (ironically because they don’t like how Blue Maryland has become!). The Washington, D.C. metropolitan area has become so dependent on the Federal Government that any significant cuts in the budget will send real estate values plummeting in Montgomery and Fairfax counties. Those residents will not take that possibility lying down. In other words, a Romney win means less money in their pockets. The fact that Obama is narrowly leading in the current VA polls speaks volumes of the effective strategy of government expansion this Administration has employed.
You are overcomplicating it. Nothing has changed in Northern VA compared to past election and McDonnell won handily against his white democrat opponent. It has always been stuffed with limosine liberals and always will be. The reason Doug Wilder won Virginia 25 years ago, the reason Obama won Virginia in 2008, and the reason Obama leads in Virginia is because of his race. Virginia is still basically a red state. If Clinton were on the ballot instead, s/he’d lose by 10. The only way Romney wins Virginia is if he can take Hampton Roads by a large number and the only way he can do that is with Petraeus or some other military type.