
The first thing that jumps out at me is that more than half the pick-ups were very Republican districts. These were districts that were opportunities in most years, but in a favorable Republican year they were able to pick them up. Of the 36 Dark Red or Light Red districts Republicans held 32 of them for at least six terms until the Democrats had their wave election in 2006. Any seat you only lose when the environment is favorable to the other side is a good pick-up. While the Republicans held 89% of all red districts, and still hold 61% of them, only 15% of the purple to blue districts were held for even four terms. We don’t need to look at analysis to tell us that the more Republican a district is, the more likely the GOP is to hold it. While the sample size isn’t great, the difference is far greater than I’d expect it to be.
Here’s are the districts the Democrats won in 2006:

While 64% of Republican pick-ups in 1994 skewed Republican, only 8% of the Democratic pick-ups did. Wave elections swing back when circumstances are more normal. Because Republicans picked up Republican seats they were able to hold onto most of them. The Democrats are unlikely to be so lucky. Here are the 95 seats that pretty much everyone agrees are in play:

Democrats picked up 20 red seats in 2006 and 2008. The maximum Republicans should pick up this year is 7. That bodes much better for Republican chances to hold the seats. In 2012 there will be a new census and new congressional districts. There are some large states (California, New York, Illinois, Massachusetts) where Republicans have the possibility of unfavorable gerrymanders that’d make the seats difficult to retain. In addition, there are several states (Iowa, New Jersey, Ohio, Pennsylvania, Michigan, Minnesota) which will lose congressional seats. The district won might be lost regardless of the redistricting.
