Andrew Gelman is puzzled at Mickey Kaus and Charlie Cook:
The myth of poor Democratic performance in House races in the 2008 election | Red State, Blue State, Rich State, Poor State: There’s an idea going around that the Democrats turned in a disappointing performance in Congressional races this year. For example, a politically-minded friend of mine of the liberal persuasion wrote: “The election was good news, although the Democrats did not do quite as well in the Senate and House as I expected. Obama did not have very long coattails–given how anti-Republican Americans are these days.” Some of the pros say this too; for example, Charlie Cook writes, “given the strength of the top of the ticket nationally, one might have thought that the victory would have been more vertically integrated. . . . what happened down-ballot was not proportional to what happened at the top.” And Mickey Kaus attributes this to moderate ticket-splitters...
That Mickey Kaus gets something wrong is not surprising--why oh why can't we have a better press corps?--but it is surprising for Charlie Cook.
Andrew goes on:
The only trouble with this theory is that it’s not supported by the data. Obama won 53% of the two-party vote, congressional Democrats averaged 56%. The average swing of 5.7% from Democratic congressional candidates in 2004 to Dems in 2008 was actually greater than the popular vote swing of 4.5% from Kerry to Obama. Let’s look at what happened state by state.... In the states in the upper left of this graph, the Democrats improved more in the congressional than in the presidential vote; the states in the lower right are those where the Obama-Kerry swing was greater than the Democrats’ swing in House races. There are a lot more states in the upper left than in the lower right....
For some historical perspective, here are the Democrats’ two-party vote share in presidential elections and average two-party vote in congressional elections since 1946:
Presidential voting has been much more volatile than congressional voting (incumbency and all that). This makes the Democrats’ 5.7-point gain over two elections even more impressive.... I don’t think it makes a lot of sense to consider Obama’s 53% “enormously impressive” and congressional Democrats’ 56% a disappointment. The data demolish the idea that voters in 2008 were pulling the lever for Barack but not for the Dems overall (not for “Nancy Pelosi,” if you will).