Based upon how residents of each congressional district voted in the past three presidential elections, House Democrats currently hold 68 Republican-leaning seats. Of the 68 Democrats holding these seats, 59 are running for reelection: 31 voted for Obamacare, 28 of these members of Congress voted against it.
Real Clear Politics (RCP) has published polls for 35 of these contests, and the RCP polling averages convey the following: The Democrats who voted against Obamacare are currently projected to win 8 races, lose 5, and win by an average margin of 5 percentage points. The Democrats who voted for Obamacare are currently projected to win 5 races, lose 16 (with 2 ties), and lose by an average margin of 3 percentage points. That’s a projected winning percentage of 62 percent for those who opposed Obamacare, compared to 26 percent for those who supported it.
If the winning percentages currently being projected by the polls hold up, it would mean that 11 of the 28 Democrats who opposed Obamacare, and 23 of the 31 Democrats who supported it, would lose. If the Democrats were also to lose 6 of the 9 races in Republican-leaning districts in which they won’t enjoy the advantages of incumbency (RCP has published polls for 3 of these races, and each shows the GOP candidate winning by at least 16 points), then that would mean that Republicans would pick up 40 seats before even stepping onto Democratic turf.