A dramatic reversal of fortune in Virginia’s 9th Congressional District, where Republican challenger Morgan Griffith appears to have awoken after 3 months of polling at 40% and today, 7 days until votes are counted, vaults into a tie with incumbent Democrat Rick Boucher, who had been sailing to a 16th term.

In a SurveyUSA poll conducted exclusively for WDBJ-TV in Roanoke, it’s Griffith 47%, Boucher 46%, within the survey’s theoretical margin of sampling error. Griffith’s lead may or may not be statistically significant; the contest should be reported as even.

Among traditional midterm voters — those who vote in most or all congressional elections — Boucher is nominally ahead, by 3 to 5 points. But: among the group of voters who tell SurveyUSA they are uniquely motivated to vote in 2010, the Republican leads almost 2:1. The relative sizes of these groups will determine the winner. If the uniquely motivated 2010 voters walk-the-ballot-box walk, and don’t just talk-the-pollster talk, the Republicans have a chance to snatch the seat. If the uniquely motivated voters aren’t so motivated after all, Boucher keeps the seat.

Compared to 4 previous tracking polls, Independents have broken sharply Republican in the campaign’s final week. The number of Republicans crossing over to vote for Boucher has steadily decreased, from 26% in July to 18% today. The number of higher-income voters voting for Griffith has steadily increased, from 43% in July to 49% today. Boucher’s lead among women has evaporated from a once 23-point advantage. The older the electorate, the better Boucher’s chances.