Based on preliminary exit poll data Tuesday night, we were able to say with some certainty how the 2014 electorate compared with 2012 and 2010. In short: It had more white, older voters — the sort of voters more likely to vote Republican.
As it turns out, the effect of that shift was multiplied by the fact that voters across the board were more likely to support Republicans than in past elections. The graph below compares the margin of support among demographic groups for Republican candidates in 2014 with support in 2012 for Mitt Romney and in 2010 for House candidates, according to exit polls.
Support for Democrats was down slightly among black voters. In 2012, black voters backed the president by an 87-point margin; in 2010, black voters supported Democratic House candidates by 80 points, per exits. Last night, they backed Democrats by 79 points. Reduced support plus reduced turnout multiplies the effect for Republicans.
Note the big swing in the Asian voting bloc, too. In 2012, strong support for the president among Asian-American voters was a surprise. Asian voters preferred the president by 47 points. In 2014, the (low turnout) group split about evenly. It was a 46-point swing.
Another way to look at the change is below. It shows the split in support among each group, with bars scaled to the percentage of the electorate that each group comprised. Switch between the elections and watch how the density of the red and blue blocks shifts.
Elections come down to turnout, yes, and Tuesday night was great turnout for the Republicans. But when every demographic group votes more heavily in one direction than two years prior, that effect is multiplied significantly.
And you have your wave.