If you looked closely at the charts I posted earlier comparing incumbent party support to GDP growth in 31 international elections, you might have noticed something interesting: In America, Democrats underperformed in the 2010 election. They did worse than the economy predicted they would do by three percentage points. Political scientist Larry Bartels, who worked up the graph in question, thinks he knows why: the health-care law and the cap-and-trade vote.

House Minority Leader Rep. John A. Boehner (R-Ohio) spreads his hands in mocking disbelief at the applause as President Obama addresses a joint session of Congress. (Linda Davidson/THE WASHINGTON POST)

Perhaps surprisingly, McGhee found that TARP didn’t do much damage, possibly because so many Republicans supported it. But voting for the stimulus cost a Democrat 2.8 percent at the polls, voting for health-care reform cost them 4.5 percent, and voting for cap-and-trade shaved 2.1 percent.

The stimulus, Bartels says, is hard to look at through that sort of analysis, as if it hadn’t gone into effect, the economic crisis would have been worse, and that too would have hurt Democrats at the polls. But the same can’t be said for cap-and-trade and the health-care law. And together, McGhee’s estimates suggest that the two policies did Democrats enough damage to account for the discrepancy between their actual vote loss, which was 8.4 percent, and their expected vote loss, which was 5.2 percent. In fact, if you account for the fact that only about half the elections featured a Democratic incumbent, the numbers match up precisely.

“While the exactness of this correspondence is no doubt coincidental,” Bartels concludes, “it does suggest that the Democrats’ apparent under-performance in the 2010 election may have been attributable to policy choices largely unrelated to the economic crisis.” Which is not say that voting for those policies was necessarily the wrong decision. If you believe those were good bills, as many Democrats did and do, then they may well have been worth the political cost. But there does appear to have been a substantial political cost.