Virginia was key to the Democrats’ winning coalition at the presidential level in 2008 and 2012. When Obama carried the state in ’08, he became the first Democrat to do so in over four decades. The commonwealth also served as one of the few bright-spot battlegrounds for Hillary Clinton, who carried it last year by five percentage points, outperforming her national numbers. But African-American turnout dropped slightly in 2016, a factor that will be critical for Northam, a former pediatrician who served in the Army as a physician. Obama’s appearance in Richmond will be aimed at this key constituency as well as young voters.

“One concern that is kind of hard to be able to analyze is: Where is African-American turnout for Democrats? Barack Obama becomes a very nice surrogate … where [attracting] those extra few votes really could count,” says Geoffrey Skelley, an elections analyst at the University of Virginia’s Center for Politics.

Northern Virginia, Skelley adds, “is perhaps the most critical part to the entire ballgame for Democrats. If turnout [there] lags in some way, that could be game-over for Democrats.”