Analysts are reading Tuesday’s tea leaves, predicting what the off-year election results mean for the presidential race. But one victory is beyond dispute. Former Attorney General Eric Holder will be celebrating this week for a decade.

Democrats on Tuesday won total control of Virginia’s government, adding both chambers of the General Assembly to the governor’s mansion. They will redraw Virginia’s legislative district lines after next year’s census. The Old Dominion was already moving left, though the redistricting power likely...