There's no question that the GOP outperformed expectations for the House last night by picking up more than sixty seats. The Douglas Hibbs model, which doesn't include contemporaneous political factors, predicted a 45-seat pickup (PDF); the median pre-Labor Day forecast among political scientists compiled by John Sides was 43 seats; and the median pre-Election Day forecast among 538, Stochastic Democracy, and Sam Wang was 54 seats. Personally, I expected substantial Democratic losses but not a 1994-style wave in the fall 2009-spring 2010 period before revising my expectations downward in April and again in September.
Senate forecasts are more difficult due to the small sample sizes, but going into last night the GOP was predicted to gain approximately seven seats; they appear likely to pick up six.
To put the historic nature of the House seat change in perspective, here are post-WWII seat losses by the president's party in midterm elections (I'm using the 538 estimate of a 65-seat loss when all the votes are counted):
The number of seat losses is a record in the postwar era.
However, it's important to keep in mind that the seat losses suffered by the president's party are partly a function of the number of seats held by the party entering the election. In this case, the relatively large Democratic caucus in the current Congress means that the proportion of seats lost, while still a record, is roughly comparable to 1946, 1958, 1974, and 1994:
While it's still very early, exit poll results suggest that the pro-GOP swing was relatively widely shared across demographic groups -- here are two New York Times visualizations from the slideshow currently running on their homepage:
As I emphasized yesterday, Obama's House majority was especially vulnerable due to the number of seats held by Democrats that had supported John McCain in 2008 (48 in all). The proportion of seats held by the president's party that supported the opposition's presidential candidate was the highest since Bill Clinton in 1994 (when Southern districts that supported Republicans for president started electing Republicans to Congress):
As expected, Democrats performed extremely poorly in these vulnerable seats and only performed moderately well in seats that Obama narrowly won (I'm using CNN's projected winners as of 10 AM EST - races that were still rated too close to call are excluded):
The political scientists Seth Masket and Steven Greene found that Democrats who supported health care reform in relatively conservative districts were underperforming those who had opposed it. To assess the initial support for this hypothesis, I disaggregated incumbent Democrats by their final vote on health care reform and Obama's performance in their district:
Democrats who supported health care reform did indeed seem to perform worse in the districts that supported McCain, though further analysis is required to determine whether the health care reform was responsible for that difference. (It might be, for instance, that anti-HCR Democrats compiled an overall legislative record that was a better fit for their districts.)
Finally, given claims that the Tea Party cost the GOP Senate seats in Nevada and Delaware, it's worth briefly following up on my post on Tea Party-endorsed candidates for the House. I previously found that Tea Party groups backed relatively experienced candidates in competitive House races. When we disaggregate Tea Party-endorsed candidates by race type (challenger or open seat) and Obama's vote in the district, we see a similar pattern -- Tea Party-endorsed GOP candidates won at a similar rate to other Republicans:
As I argued yesterday, it's important to keep these results in perspective. While Republicans face a relatively favorable path to retaining control of the House and gaining control of the Senate going forward, this election is not a realignment and will not create a permanent Republican majority any more than the 2006 and 2008 elections did for Democrats.
Follow Brendan Nyhan on Twitter: www.twitter.com/brendannyhan