There was much speculation at the time of the passage of the Affordable Health Care for America Act that a yes vote might put Democratic House members from moderate districts in greater danger of electoral defeat. Voters are known to punish members for being ideologically out of step, but would one particular roll call vote matter? (Steven Greene suggested this idea to me -- blame him for this particular act of inception.)
To see how House members were doing, I used 538.com's brilliant election forecasting site.* I decided to look at the members from the 50 most conservative congressional districts (as measured by the 2008 vote for McCain) that are represented by Democrats. These range from Florida's 22nd (represented by Ron Klein), where McCain got 48 percent of the vote, to Mississippi's 4th (represented by Gene Taylor), where McCain pulled 68 percent.
Out of the original 50 districts, only 41 had members who cast a vote on health care reform and are running for reelection. If we just divide these members based on their health care votes, those who voted for health reform are running 2.7 percentage points behind those who voted against it. But, of course, we should control for other things, especially district conservatism, since those from the more conservative districts voted almost uniformly against reform. I also included the members' DW-NOMINATE scores to distinguish the health care vote from the members' overall voting records.
What I found was that Democratic supporters of health care reform are running 3.2 percentage points behind Democratic opponents. (This is statistically significant at the p≤.05 level.) That's a three percentage-point penalty resulting from a single roll call vote. I would describe that number as large. Most members of Congress win by much greater margins than that, of course, but for Democratic incumbents from conservative districts in a distinctly anti-Democratic year, three points is serious business. Indeed, of the 41 Democrats I examined, only six are currently forecast to win by more than three points (and none of those voted for health care reform).
*The 538 forecasting site is far from perfect, and I question some of their results. For example, they suggest that Rep. John Salazar in Colorado's 3rd will only get 48 percent of the vote, which I think understates his support significantly. But they're depending on polling, which is pretty scant in most congressional races. Regardless, 538's site is far and away the best thing going on out there in terms of House election forecasting. Thanks to Wesley Hussey for the tip.
Update: The data are available here.