Brendan Nyhan finds that vulnerable House Democrats who voted against the main Democratic agenda items did better, controlling for circumstances, than those who voted for it:
[C]onsider Eric McGhee's post on The Monkey Cage. Consistent with my finding that Democrats from competitive districts who supported health care reform appeared to perform worse on Election Day, he finds that House Democrats who supported health care reform, TARP, the stimulus bill, and/or cap-and-trade performed worse than those who did not controlling for the partisanship of their district. This finding directly contradicts the simplistic claims above about the effects of health care, cap-and-trade, and the Blue Dog agenda.
I replicated this estimate* and it appears to be robust. To illustrate the finding, here is a plot of the estimated marginal effect of an additional vote for one of the four controversial bills. I restrict my analysis to Democrats in potentially competitive seats (i.e. where President Obama received less than 60% of the vote in 2008):
The y-axis represents the estimated effect of an additional vote for a controversial bill on the predicted Democratic vote. The plot shows that this effect becomes increasingly negative as the district becomes less favorable to Democrats (lower Obama vote in 2008).
I think this is good evidence that vulnerable Democrats were better off breaking with their party on key votes. But I think Nyhan is wrong to conclude that "the Democrats' aggressive legislative agenda may have provoked a backlash that was at least partly responsible for GOP overperformance in the House."A party in power needs to have an agenda of some kind. If you don't do anything major, then voters just get angry that you're not doing anything while the economy plummets. (See Bush, George Herbert Walker.)
Now, what the agenda is obviously matters. But it's also the case that voters often pay scant attention to the details of these bills. But they do get a general sense of what the big battles are and who's on what side. If you're a vulnerable Democrat, you need to signal opposition to the national party. Otherwise you're just a big government liberal just like the ones who hate guns and like gay marriage. Some Democrats failed to demonstrate their independence from the national party by dissenting on major partisan issues, but that doesn't mean the issues themselves were the problem.