Cook Political Report reports:
The Cook Political Report's House editor and chief number cruncher, David Wasserman, reports that Obama carried only 690 counties last year (fewer than Michael Dukakis's 818 in 1988), compared with Mitt Romney's total of 2,424. That is how concentrated the Democratic vote is in population centers. Between congressional retirements and wave elections, very few Democrats now represent districts that God didn't intend for a Democrat to hold, and few GOP members hold seats not intended for a Republican. The Senate isn't quite as bad as the House in this regard, but there are plenty of one-party states, as well.
There's more:
Only once since the end of World War II has the percentage of House members successfully seeking reelection dropped below 80 percent; that was when it dipped to 79.3 percent in 1948. In the more volatile Senate, in six of the seven elections between 1946 and 1958, the percentage of senators who sought reelection and won was below 80 percent. From the 1960s onward, the Senate's reelection rate has usually been in the 70s and 80s, occasionally the 90s. But it did drop to the low-to-mid-60s in the 1976 and 1978 elections and then to 55.2 percent in 1980, a three-election sequence that stands out in volatility.
Only three times since 1980 and eight times since 1946 have 10 or more House members lost renomination; five of those eight times—including 2012, when 13 members lost their primaries, and 1992, when 19 did—were in the first elections after redistricting, when incumbents are sometimes forced to run against each other. Only in four elections since 1946 has the number of senators losing primaries numbered four or more; the last time was in 1980.
The incumbent protection racket.
