BlueLabs’s analysis showed that Mr. McAuliffe’s margin would have expanded by an additional 5 points if turnout had been equivalent to that of the 2012 race.

That analysis is consistent with the precinct-level results. Turnout fell by more than it did statewide in heavily Democratic precincts — usually with an overwhelmingly African-American population. The decline wasn’t as steep as in 2009, but it could not be mistaken for the 2012 electorate either.

This doesn’t mean the Democratic turnout operation was ineffective. It helped on the margins. After all, the Virginia electorate was more favorable for Democrats in 2013 than it was in 2009.

But Mr. McAuliffe’s win was narrow — especially considering the tepid Republican effort. And no Democratic turnout effort will revitalize the so-called Obama coalition of young and nonwhite voters in an off-year election. The levels of voter interest in a midterm election and presidential election are simply too different. Indeed, Mr. Kreisberg said the McAuliffe campaign didn’t aim to match 2012 turnout; it was mainly focused on outperforming turnout in 2009.

As a result, Democrats might not be able to follow Mr. McAuliffe’s footsteps this year. Mr. McAuliffe needed to overperform among well-educated, affluent voters in Northern Virginia to squeak out a victory, and not every Democrat will be lucky enough to receive a gift like Mr. Cuccinelli or to run in a state won by Mr. Obama.

To hold the Senate, Democrats will need to overcome their turnout problem the old-fashioned way: win older, white voters at far greater rates than Mr. Obama did.

That’s how Democrats used to deal with low midterm turnout among young and nonwhite voters, who have never turned out in off-year elections, not even in 2006, when Democrats were said to be especially energized.