The 2014 elections were decided by those who actually showed up to vote. But the Pew study was a survey of adults, not just registered voters, or those who cast ballots. And so the most striking aspect of the study is just how Democratic the population remained in 2014, even during a year in which Republicans swept elections nationwide. It highlights a striking gap between those who voted and the general population; the electorate was significantly older, and more Republican. Millennials, for example, made up more than 20 percent of the Pew survey but a smaller chunk of the voting public, according to exit polls. And party identification among 2014 voters was almost evenly split, despite the Democrats’ longstanding advantage in surveys.

Some pundits declared that an artifact of weak turnout in midterm years, in which many of the Democrats who twice elected Barack Obama stayed home, skewing the results in favor of the more reliable Republican base. Others pointed to the GOP win as evidence of a more significant rightward shift, one that can be replicated not only in congressional elections, but also in the 2016 presidential race. The results of individual congressional races can be difficult to generalize, as voters who lean toward one party or the other may be drawn to particular candidates, or disinclined to vote in uncompetitive races. But whatever the cause, the Pew survey suggests that the result was a Republican Congress, governing a nation that tilts toward Democrats.