Another powerful lesson is that even with the best technology, Democrats remain dangerously dependent on a boom-and-bust coalition of young people and minorities, whose turnout is much lower in midterms than in presidential elections. Despite overheated predictions, Democrats performed almost exactly as well with millennial voters (including whites) and most minorities as they did in 2010 (although their performance did decline among Asians). But the share of the vote cast by those under 30 was 6 percentage points less in 2014 than in 2012; the minority share dropped 3 points. On both fronts, the pattern exactly followed the sharp falloff from 2008 to 2010, despite this year’s huge Democratic investment in turnout.

That suggests Democrats cannot compete for Congress without more support from middle-class and older whites. In the national House exit poll, Republicans carried exactly three-fifths of whites, virtually unchanged from 2012 and 2010. That advantage was remarkably consistent. The only Democrat in a top-tier Senate race who carried a majority of whites was New Hampshire’s Jeanne Shaheen, who won. Continuing their contemporary pattern, whites over 45 and those without college degrees broke especially hard against Democrats.

With their Senate victories in Colorado and Iowa, their strong showing in Virginia, their blue-state gubernatorial breakthroughs, and their competitive performances in several previously Democratic-trending suburbs, Republicans powerfully reasserted their ability to compete nationally. But winning governorships doesn’t consistently predict presidential success in a state. And unlike in 2010, the GOP did not capture any new Senate seats from the 18 “blue wall” states underpinning the Democrats’ Electoral College advantage. Even if Republicans in 2016 match Tuesday’s dominant three-fifths showing among whites, they will almost certainly lose the White House if they can’t also narrow the Democrats’ traditional presidential-year edge with minorities—who could make up 30 percent of the electorate by then.