"Off-year" electorates such as this one typically show lower turnout than midterms or presidential years (only 45 percent of registrants turned out for the last gubernatorial contest in 2005, compared to 75 percent who did in 2008) -- but it is the shape of the electorate that will matter just as much here, as well as what happens in a couple of key regions of the state that have led the state from reliably Republican to toss-up in recent years.
Specifically, watch the percent that is African-American – it was 20 percent in 2008, and reliably Democratic -- benefiting both Barack Obama and Mark Warner. Also watch the percent that is young. Last year, one in five voters was under age 30, and they went overwhelmingly for Mr. Obama as well.
Without Deeds getting strong turnout showings from both these groups, McDonnell could be set to capitalize on a relatively older and more conservative electorate much more favorable to a Republican.
Perhaps the best-known regional component of the Democrats' recent winning "formula" for Virginia is the northern area of suburbs of Washington, where growing ranks of professionals and more moderate-to-liberal upper-income suburban voters have trended Democratic over the last decade or so, similar to a swing that's taken place in the Northeast and other high-growth areas of the country.
Centered around and beyond Fairfax county, this is a region that has given recent successful Democrats (including Mr. Obama, current Gov. Tim Kaine and Senator Sen. Warner) about six in ten of its votes in their wins. And as the region has grown, about one in five of all the state's votes have been cast there.
But whether Deeds can win by similar margins here, replicating the success of Mr. Obama and Kaine before him, remains one of the central questions of the race and could tell the tale of the final outcome. Even if McDonnell just comes close in the region -- perhaps in the mid-forty percent range or better -- it could be well be enough.
Watch Loudoun county in particular – it's the fastest growing county in the state which both Kaine and Mr. Obama carried -- and Prince William too. If that McDonnell can reverse trends there, it will be a key step for him.
And this is as much about percentages as raw numbers and turnout – Deeds not only needs to win up north, but he also needs to rally voters to turn out in order to drive up large vote margins if he does.
Finally, western Virginia will tell an important story, too. Of late, Democrats have made their gains in the north hold up by running relatively well (even if losing) in this more conservative region of the state. Jim Webb held his own, and Mark Warner famously did very well in appealing to these conservative voters. Deeds is from the region and might be expected to perform well, too – but if McDonnell does well in the west it would be an essential part of his crafting his own, new winning formula for the GOP this year. How the statewide electorate compares to 2008's will be central to knowing whether he does.
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Anthony Salvanto is CBS News Elections Director. Mark Gersh is Washington Director, National Committee for an Effective Congress, and a CBS News Consultant.