As the Monkey Cage notes, there are only two dozen seats currently represented by Democrats where President Obama took less of the vote than his national average. Here's a few other data points that speak to the decided dearth of even remotely competitive seats in the House:
* There are a total of 77 districts -- 17.7 percent of the total House -- where the current member was elected with 55 percent or less of the vote in 2012, according to tabulations by the non-partisan Cook Political Report. But, less than half that number --33 -- are places where the incumbent won with 52 percent or less. (Of that 33, 19 are held by Democrats, 14 by Republicans.) If you take 52 percent and under as the true mark of seats that would switch sides in any sort of wave election scenario, you are talking about 7.5 percent of the total House.
* According to Cook's Partisan Voting Index (PVI), a measure of the relative partisanship of every district compared to every other district, there are only 15 Democrats sitting in seats with a Republican PVI score (meaning the seats vote more Republican than the country as a whole) and just five Republicans sitting in seats with a Democratic PVI score. There are nine more districts -- six held by Democrats, three by Republicans -- that are rated as having an "even" PVI, meaning they are right in the center of the national electorate. That's 29 seats out of 435 -- or about six percent of the entire House.
There's also this historical fact: In the 16 elections since 1982, only three --1994, 2006 and 2010 -- have produced net House gains of more than 30 seats for one party. The tendency in the political community is to assume the recent past is everything -- and that tendency means that we focus on the nationalized elections of '06, '08 (a 21-seat Democratic gain in what most observers categorized as a national wave) and '10 as the rule rather than exceptions to it. Time may show that to be true -- we are living in unprecedented political times -- but you could also make the argument that 2006-2010 was an anomaly while what happened in the elections between 1996 and 2004 -- in which the average pickup was four House seats -- remains the rule.
Viewed broadly, there just aren't that many districts that a wave could wipe away. That's not say, of course, that Democrats have no hope of picking up the 17 seats they need to win back the House since such a gain would fall fell short of our traditional definitions of a wave election. What is clear --from the Monkey Cage model, the Cook data and a look back at history -- is that the vast majority of the 435 House seats are now located far in the political inland, entirely protected from even an epic wave.