In case Republican candidates need confirmation that Obamacare was and is a huge vulnerability for the president and Democrats, a new study suggests that, of all the contentious votes taken in the president’s first two years in office, how a House Democrat voted on Obamacare was the most important predictor of whether he would retain his House seat. The Fix’s Aaron Blake relates:

The study ran 10,000 simulations of a scenario in which all vulnerable Democrats voted against the health care bill and found that the rejections would have saved Democrats an average of 25 seats, which would have made the House parties close to a tie. (Republicans won 63 seats overall, but the study suggests around 25 of them would have been salvaged.)

In 62 percent of the simulations, Democrats were able to keep the House.

The study uses district-level data to show that the vote created “ideological distance” between the Democratic members of Congress and the median voters in their districts, compared with similar districts where the Democratic incumbent voted against the bill.

“Democratic incumbents who supported health care reform were seen as more liberal on average by their constituents than those who did not,” the study says.

House Democratic whip Steny Hoyer also recently acknowledged that Obamacare was “clearly a liability” in the last election. By November, two more years will have passed and voters will likely have begun to think that, if they haven’t yet experienced any dire consequences of Obamacare, then they never will. But many of the bill’s most controversial provisions don’t take effect until 2014. As Blake writes, Obamacare is “a sleeping giant,” and, if Republicans don’t rouse and slay it now, repeal not only will be impossible — but, from 2014 onward, the giant will wake to ravage a nation lulled into a false sense of security by the passage of time.