House Republicans enjoy an exceptional advantage in the form of gerrymandered districts. In the 2012 elections, Democrats won the national popular vote by 1.5%, but they needed a 7.3% margin to take control. So broadly speaking, opinion would have to swing by about 6% or more for control of the House to become competitive.
It is said that public opinion has not swung as hard against Republicans as in 1995. But that statement is based on questions that ask who is more to blame, Congress or President Obama. President Obama is not up for re-election in 2014. A more relevant number is the generic Congressional preference, which tracks the national vote fairly well. Before the shutdown, three generic Congressional preference polls taken Sept. 23-29 (Quinnipiac, Rasmussen, PPP) show an average of Democrats +6.0+/-1.5%. That's a swing of less than 5%. This is the last snapshot we have before the shutdown.
More recently, a provocative set of district-level polls was conducted for MoveOn by Public Policy Polling (D). These are partisan organizations, but I note that of major pollsters, PPP had the best accuracy in 2012. Also, even the worst house biases are no more than 3 percent. As we will see, even that is not enough bias to alter the conclusions here.
PPP surveyed 24 congressional districts currently held by Republicans. They asked voters to choose between their current representative and a generic Democrat (data as PDF). Here are the margins they got, plotted against last November's election result:.
The swing was toward Democrats for 23 races (below the red diagonal) and toward the Republican for one race (above the diagonal). The key piece of information is the gray zone. If more than half the points are in that gray zone, then that predicts a swing of >6% and a Democratic takeover. Currently, 17 out of 24 points are in the gray zone.
Individually, the district-by-district swing is quite variable, +4% to -23% (where + indicates a swing toward Republicans). But the average is clear, -10.9+/-1.5% (mean+/-SEM). That predicts a national popular-vote margin of D+12.0%.
Since the election is over a year away, it is hard to predict how this will translate to future seat gain/loss. If the election were held today, Democrats would pick up around 30 seats, giving them control of the chamber. I do not expect this to happen. Many things will happen in the coming 12 months, and the current crisis might be a distant memory. But at this point I do expect Democrats to pick up seats next year, an exception to the midterm rule.
Note that in these calculations I did not even include the worst of the news for Republicans. In a followup series of questions, PPP then told respondents that their representative voted for the shutdown. At that point, the average swing moved a further 3.1% toward Democrats, and 22 out of 24 points were in the gray zone. That would be more like a 50-seat gain for Democrats - equivalent to a wave election.
Of course, the big question is how the current snapshot, a probable House turnover to the Democrats, will evolve in the coming 12 months. At the moment we are in territory that resembles 1995, a shutdown with blame going largely to congressional Republicans. If the government is funded with a continuing resolution (CR), then opinion could easily swing back and the GOP could hold on to the House. But what if the government hits the debt ceiling? In such an extreme circumstance, which has been called the domestic equivalent of the Cuban Missile Crisis, the outcome I have calculated here becomes quite a plausible scenario.
At this point, an analyst would have to be crazy to predict that that will happen. However, it seems like mandatory information for a Democratic campaign strategist - or any Republican incumbent who won by less than 20 points in 2012.
Sam Wang is an associate professor of neuroscience and molecular biology at Princeton University. He is also co-founder of the Princeton Election Consortium.