Nate Cohn measures it. Democrats now need 32 seats to retake the House:
The Republicans hold only 28 seats in districts that were carried by Mr. Obama. Many of these seats would fall to the Democrats in an anti-Republican year. The 12 newly elected Republicans who won seats in districts carried by Mr. Obama in 2012 are particularly vulnerable; many of these freshman Republicans could lose re-election in 2016.
Yet Democrats will have a struggle to win all of the seats held by Republicans that voted for Mr. Obama in 2012. The benefits of incumbency will allow many of these Republicans to defy even the most inhospitable conditions. And some of these Republicans, like Dave Reichert of Washington or Frank LoBiondo of New Jersey, are survivors of the 2006 and 2008 waves.
He concludes that “a Republican president is probably a prerequisite to a Democratic House.”
Cohn, whose polling and demographic analyses are usually top notch, might be right this time, assuming that Republicans make no mistakes and Democrats keep shooting themselves in the foot. The last round of redistricting certainly gave Republicans a boost, and their expanded control of state legislatures may give them a head start on the redistricting that will take place after the 2020 census by boosting their likelihood of retaining control of those chambers. The expanded control at the state level also means that Republicans will produce more experienced candidates for the House and Senate over the next few years, which is one reason why some Democrats pointed to that outcome as the worst news from Election Night.
Still, history cautions against Republican optimism and Democratic despair. As we have seen over the last 20 years, it’s usually folly to assume that parties can avoid overreach and scandal for very long. Turnout in this wave election was historically low, which argues against learning any significant lessons on demography and sustainability. Unlike 1994, Republicans did not run on a unifying national platform; they relied instead on deep dissatisfaction with President Obama and Democratic leadership in the Senate that refused to check his perceived abuses. That parallels 2006 most closely, which means that the one mandate Republicans can claim would be to force Obama to work with the GOP on their terms, as voters either turned out to oppose Obama or didn’t bother to turn out in his support. That mandate could mean an even higher risk of overreach, although the lack of electoral consequences for last fall’s government shutdown suggests voters are very fed up with the White House.