Four out of every five House members who didn't side with their party on the health care bill represent districts that voted for the opposite party's presidential nominee in the 2008 election.

The party-buckers on the 220-215 vote on Saturday night included 39 Democrats who voted against the bill. Of them, 31 represent districts that voted for John McCain over Barack Obama. Republicans are targeting many of them for defeat in the 2010 election. Of the other eight, three are serving their first terms in districts in which they defeated or succeeded Republicans in the 2008 election.

Eighteen Democrats from McCain-voting districts backed the bill. Among this subset, seven-term Rep. Marion Berry of Arkansas represents the most pro-McCain district (59 percent). He's more politically secure than other "McCain Democrats" who voted for the bill, including first-term Rep. Tom Perriello of Virginia and second-term Rep. Zack Space of Ohio.

The campaign arm of Republicans in the U.S. House is using this week's legislative recess to criticize some Democrats who backed a climate change bill the House narrowly passed last week.

The National Republican Congressional Committee's advertising campaign consists mainly of low-cost radio advertisements and telephone calls against 14 Democrats, most of them from conservative-leaning districts, who helped provide the winning 219-212 margin in the June 26 vote. Eight Republicans also backed the climate change bill, which most Republicans described as a massive "national energy tax" on consumers.

A top target of the NRCC campaign is first-term Virginia Rep. Tom Perriello, who broke with most politically vulnerable Democratic freshmen in backing the bill. The NRCC is airing a television ad in Perriello's south-central Virginia district that urges viewers to "tell him he was wrong to vote for the [Speaker Nancy] Pelosi energy tax."