In 2016, a critical question facing both sides is whether the eventual Democratic nominee can “continue to energize and turn out nonwhite voters” as effectively as Obama did, notes Alan Abramowitz, an Emory University political scientist. But whatever happens in 2016, the long-term trend is that more minorities in the pool of potentially eligible voters will translate into a rising minority share of the actual vote on Election Day. “This is a very long-term trend that has been going on over many elections,” says Abramowitz. “If you project beyond 2016, to 2020 and 2024, there is no question the white share of the electorate is going to keep declining. It’s just math.”

Obama’s share of the vote among whites dropped in all five Sun Belt swing states from 2008 to 2012. Democrats are optimistic that Hillary Clinton, as potentially the first female nominee, could reverse that decline in 2016. But if Democrats can’t stop their slide among whites (who also broke sharply toward Republicans in each of these states in 2014), the central question across the Sun Belt next year might be: Which declines more—the share of the white vote Democrats are attracting, or the share of the white vote they need to win?

Diversity is also spreading, but much more slowly, in the six Rust Belt swing states (Iowa, Michigan, New Hampshire, Ohio, Pennsylvania, and Wisconsin). Compared with 2008, the model projects that by 2016 the white eligible voter share will drop in a range from Pennsylvania at the high end (3.1 percentage points), to New Hampshire at the low end (1.2 points). Behind strong Obama turnout efforts, from 2008 to 2012, minorities in Ohio and Pennsylvania grew even faster as a share of actual voters than as eligible voters. That helped Obama win Ohio in 2012, despite attracting exactly the same share of the white vote (41 percent) that Gore did and less than Kerry did (44 percent) when each lost the state in 2000 and 2004 respectively. (Obama also held Pennsylvania, despite winning considerably less of the white vote than either Gore or Kerry, who both carried the state.) But, overall, racial change is not nearly as big a factor in these brawny battlegrounds as in the Sun Belt swing states.