Last Week the Cook Report issued the updated Partisan Vote Index that adjusts for the results of the 2012 election (the Cook Report releases the PVI in three tables -- by district, by member, and by partisan rank). I'll skip over most of the details in the story about the change over time in the number of swing districts to focus on what this release means for 2014.
First, the explanation of the data and the cautions on its use, the Partisan Vote Index is a measure of how far the presidential votes in a given district differ from the national average over the past two cycles. (With redistricting, the assignment of the 2008 vote to new districts is, in some cases, a rough estimate). In other words, it is, in part, a measurement of how well the people running redistricting have gerrymandered the districts, but it is also, in part, a measure of how well a party has do nationally to win an election.
Second, because it is based on divergence from the national average in the last two elections -- an "even" district is one that Obama averaged a fraction under 53% in 2008 and 2012. Thus, to win an even district, the Democrats would need to get around 53% nationally.
Third, individual Congressional races (and thus the national vote total) differ from the Presidential race in multiple ways. For Presidential races, the two parties, in theory, are each running a strong candidate. For Congressional races, especially lopsided races, a party may not be able to get any candidate much less a strong candidate. Representatives may serve the same area for twenty-thirty years becoming well-known to their constitutents and picking up voters who otherwise would never vote for a candidate from the representatives party. In some states (Louisiana, California, and Washington), candidates run in a jungle primary in which candidates from bothe parties compete against each other and the top two regardless of party advance to the general.
Fourth, while election forecasters love to talk about a uniform national swing, there is no such thing. Even with a nation race (like for the President), you can see when you compare the 2008 numbers to the 2012 numbers (a very, very tiny overall swing to the Republicans), there were districts that swung noticeably towards Romney and districts that swung noticeably toward Obama throughout the chart. When you add in the strength of weaknesses of individual candidates in congressional races, there will be Democrats winning districts that they shoujld not win,a nd losing some districts that they should win.
Having given the appropriate cautions on the limits of these numbers, what do they show. First, even with his sizable national win, President Obama only carried 209 seats in 2012. President Obama probably needed about 0.75% more to get to a majority of Congressional Districts (one reason why Republicans keep flirting with adopting the Maine-Nebraska system). Currently, the median district in the county is the Third District of Washington, showing an Index of R+2. In theory, to win this election, the Democrats need to get a national vote total of around 52.25% (compared to the approximately 50.5% in 2012). However, while theoretically, the Republicans should have only gotten 51.5% of the vote in this district in 2012 based on the national numbers, they actually got 61%. To get enough of a swing to actually get to 218, the Democrats probably need something like 54% to account for districts in which Republicans overperform and Democrats under perform (which would only put another 10-15 seats into play).
Even beyond the swing needed for this median district, the other numbers from the PVI tell a very ugly story.
Currently, Jim Matheson of Utah's Fourth District hold the most Republican seat in the Democratic caucus. Even putting aside the distorting features of having a native son on the ballot in 2012, McCain got 56% of he vote in this district in 2008. There are a total of seven Democrats from districts that both McCain and Romney carried and two from districts that Romney won. By definition, these nine are permanent targets.
On the other side fo the aisle, Gary Miller of the California's 31st District holds the most Democratic seat in the Republican caucus. Obama got 57% of the vote both times in this District. Mr. Miller, however, is somehting of an accidental by-product of the jungle primary system. So many Democrats ran in the primary that the top two finishers were both Republicans. The next closest Republcans come form D+2 districts. Overall, there are fifteen Republicans from districts that Obama won both time and two more from districts that Obama won in 2012). Even if the Democrats win all seventeen districts and hold there nine Romney seats, they just barely get to 218.
The margins in the PVI are equally ugly. If a margin between even and +2 is a pure swing seat, a margin between +2 and +5 is a lean seat, and a margin over +5 is a likely seat, the margins in the distrcts give the Republicans 222 lean and likely seats to 174 lean and likely seats for Democrats. More importantly, the Republicans only hold one of the 174 lean Democrat seats (California's 31st), but (corresponding with the number of Romney districts held by Democrats), Democrats have 9 of the lean seats.
There are only 35 pure swing seats after the 2012 election. Currently the Republicans hold a 20-15 advantage. Given the difficulty of winning additionaly lean Republican seats, the Democrats need to win at least 17 of the 20 Republican swing seats and probably all 20 to offset any possible losses of the five likely Republican seats currently held by Democrats. The bottom line of these numbers is that there is only one "easy" target seat for Democrats in 2014. Winning the majority back is going to take effort and hoping for targets of opportunities where Repulicans nominate candidates who are grossly out of touch with their districts (e.g. Michelle Bachmann who came within a hair of losing a seat with a PVI of R+10 in which Romney geto 56% of the vote).