What happened?

Jonathan Cohn of TNR explains:

It was a horrible night for the Democrats. They lost control of the Senate, which was to be expected. But they lost nearly all of the close races and appear to have held onto seats in New Hampshire and Virginia only by the thinnest of margins. Democrats also failed to oust Governor Rick Scott in Florida and Scott Walker in Wisconsin. More troubling still: Democratic candidates lost governor’s races in Illinois and Maryland. In Vermont, land of Ben and Jerry's, the Democrat barely edged his GOP counterpart but couldn't get 50 percent of the vote, sending the contest to the State Legislature. He should get elected anyway, but when Democrats are struggling in deeply blue states like Vermont, you know it's a really bad night.

Oh, and Republicans padded their majority in the House. They should have around 250 seats when final results are in everywhere.

What the heck happened? Everything that was true 24 hours ago is true now. The states with Senate races tended to be Republican-leaning, yielding an electorate substantially more conservative than the country as a whole. And turnout was lower than in presidential elections, with participation disproportionately lower among groups that vote Democratic. In 2012, as John Judis points out, voters between 18 and 44 made up nearly half the electorate. In Tuesday's elections, they were less than one-third of the electorate. Don't let anybody tell you that these two factors, geography and turnout, weren't a huge part of the story.

But they're not the whole story, as Judis also notes. Turnout among young people [was] low even by midterm standards. That suggests the Democrats, and particularly the president, failed to rally them. More generally, Obama’s approval rating is in the low 40s—better than George W. Bush in his sixth year, but worse than President Clinton’s or President Reagan’s. With those kinds of ratings, the president’s party is not going to fare well, even in states where Democrats are typically more competitive. . . .

Republicans can’t honestly claim a mandate tonight. They can’t even claim a mandate to undo Obamacare, the program that they claim to hate most. No, all Republicans did was say they were opposed to the president. On Tuesday night, that was enough to win.