Not that I want to support the return of former Speaker Tom DeLay to the public forum, but I'll note that he makes an interesting point about the Democratic Party's national grassroots organization efforts, which he says will mitigate some of the potential for Republican gains in the US House.
He might be right -- although it remains to be seen how effective that operation proves to be in a year when Democrats seem less enthused than they did in the last two election cycles.
I'll add another factor that might have some effect: prominent top-of-ticket races.
Let me back up a bit. One popular theory is that Republicans figure to do better this November when they can make their individual races into a broad referendum on Obama and the Democrats. Democrats figure to do better when they can make those races into a choice between the individual candidates -- particularly if they can get voters thinking about the lack of experience, or the disagreeable positions, of the Republican challengers.
Unlike the high-profile races, like those for US Senate or Governor, House races typically do not get a huge amount of the average voter's attention, making those races more about the parties, and making them more susceptible to the wave of national mood.
They do get closer attention from the subset of regular, informed voters -- not only do those types of voters seek out information about the candidates, the candidates (and those grassroots party organizations) seek out those voters, targeting them on their mailing, door-knocking, and phone-calling lists.
In low-turnout elections -- as is usual in mid-term elections -- those types of voters make up a larger share of the total turnout.
But -- finally getting around to my point -- there are an unusual number of competitive, high-profile state-wide elections this year, including most of the high-population states that hold the bulk of the congressional districts.
California, for example, has very competitive races this year for both governor and Senator. So do Florida, Illinois, Pennsylvania, and Ohio. That's 134 congressional districts -- including 13 of the 40 seats rated as "Toss Up" by the Cook Political Report. At least 14 more of those Tossups are in other states with at least one very competitive top-of-ticket race.
Those states should have relatively high turnout. One could theorize that this could help Republican House candidates by A) bringing more people to the polls who are voting from mood rather than knowledge of the down-ballot candidates; and B) blunting the Democrats' get-out-the--vote advantage described by DeLay.
On the other hand, one could theorize that it could help Democrats, because a low-turnout election would bring out only the most motivated voters -- which appears to be the ones motivated to vote against Democrats. A high-turnout election, then, could blunt that effect by bringing the less-motivated, Democratic-leaning voters out.
Probably all of this actually will have relatively little effect on the whole, but it's something to think about.