If SurveyUSA is accurate, Bob McDonnell is now ahead, 59 percent to 40 percent in Virginia’s governor’s race.

In the past, I’ve thought SurveyUSA’s samples had just a smidgen too many Republicans for my taste, and that may be the case here. But I also wonder if there’s a bandwagon effect going on — polls showing the Republican ahead make people who were wavering Deeds supporters to drop him and go with the likely winner.

As I said yesterday, in 1997 Jim Gilmore beat Don Beyer 55 percent to 42 percent, and in 1993, George Allen crushed Mary Sue Terry, 58 percent to 41 percent. So a margin approaching 20 percentage points is not unthinkable.

Now excuse me as I go poke fun at my Virginia sources who told me to expect some tightening in the numbers in the coming days . . .

UPDATE: Actually, the partisan breakdown of this SurveyUSA sample looks pretty reasonable: 33 percent Republican, 32 percent Democrat, 33 percent Independent, which is pretty reasonable. In 2006, exit polls in Virginia showed an electorate split 39 percent Republican, 36 percent Democrat, 26 percent Independent.