Playing with 538.com's Swing-O-Matic electoral college calculator is actually very cool, but also pretty sobering. It doesn't take much of a shift among non-college educated white voters for Republicans to win 2016 walking away.
In 2012 they voted 62% Republican, with a turnout of 57%, and Romney lost 332-206 in the electoral college. College-educated whites voted for Romney 56% with a turnout of 77%.
If college-educated white voters shifted to the Republicans from 56% to 62% Republican, where non-college educated white voters where in 2012, you're looking at a GOP president. Florida, Ohio, Iowa, New Hampshire, and Virginia would flip red and Republicans would win 276-262.
If non-college educated whites go from 62% to 67% GOP, Dems also lose. In that case, Colorado, Wisconsin flip instead of Virginia and they'd win by an even larger margin, 282-256.
Should both happen, it's an absolute wipeout. Dems would lose those states plus Pennsylvania, Maine, Nevada, and even Oregon and Minnesota. It would be a 358-180 wipeout.
Black voters would have to turn out at 92% level and vote at Obama's 93% in order to eke out a 270-268 electoral win for the Dems in that case.
On the other hand, should Democrats pick up even slightly more of the white vote, it becomes total carnage for the GOP. If non-college white voters were split 50-50, Dems would roll to a 404-134 win, and would even win states like South Carolina, Missouri, and Georgia.
So it can go either way, but it doesn't take much.