In interviewing congressional candidates, a common question that we at The Cook Political Report ask is, "What's one issue or vote on which you would differ from your party's leadership?" In this era of extremely polarized districts and elections, the ability to show distance from the pack and rise above the rubber-stamp label seems to really impress independent voters and often makes the difference in swing seats. In some places, crossing the party line on a radioactive issue is almost a prerequisite for being taken seriously.

In the June 26 House vote on cap-and-trade legislation, however, the higher-than-usual number of defections (44 Democrats and eight Republicans) indicates that something larger than just independent thinking and parochialism was at work. That so many Democrats and a few Republicans went their own way suggests genuine uncertainty and nervousness among rank-and-file lawmakers about how voters will feel in the fall of 2010 about the brand of change that President Obama is selling with the global-warming bill. The act of bucking House Speaker Nancy Pelosi, D-Calif., or Minority Leader John Boehner, R-Ohio, appealed to many members as something of an inoculation against being seen as beholden to either party's agenda.

In casting yes votes, several Republicans made a decision that takes some of the edge off potential Democratic challengers' efforts to tag them as "obstructionist" and makes the incumbents less susceptible to being lumped together with global-warming deniers in 2010 ads. But more scrutiny is due the choices of House Democrats, who stand to lose more if their party's position becomes less popular over the coming months. Of the 49 House Democrats serving in districts that GOP presidential nominee John McCain won in 2008, 20 voted for the Waxman-Markey bill; 29 voted against it. Two of the three Democrats whose 2010 prospects are rated as "toss-ups" by The Cook Report voted against, as did nine of the 20 Democrats whose seats are listed in the "lean Democratic" column.

Groups favoring cap-and-trade hail the bill's politically vulnerable supporters as profiles in courage, but opponents might say the real profiles in courage are the reasonably secure Democrats who artfully plotted leadership-proof escape routes from the House floor after hitting the nay button. Either way, as the bill advances to the Senate, questions concerning political fallout in the House have yet to be answered. First, to what extent will constituents of Democratic supporters from rural, energy-sensitive areas (read the Midwest, the South, and Appalachia) start viewing the proposal with anger rather than skepticism? And, second, will this vote foment a surge of credible GOP candidates to challenge these Democrats, many of whom have faced only token opposition in recent election cycles?

All 49 "McCain-district Democrats" outperformed the top of their ticket to earn their current terms, thanks to either their own personal appeal or their GOP challenger's weakness. A few of the 49 have admitted that they lack the sales skills necessary to have defended a yes vote.

For those who voted for Waxman-Markey, 2010 will present a real test. If the economy doesn't improve soon, will struggling voters in central and southeastern Ohio accept the Democrats' promise of the eventual creation of green jobs as an acceptable rationale for sophomore Democratic Rep. Zack Space's yes vote? Will eastern Maryland voters, who gave McCain 59 percent of their support, reward freshman Democratic Rep. Frank Kratovil with a second term after his thumbs-up? History and a quick look at the current state of play suggest that Democrats should expect to lose six to 12 seats if the political environment in 2010 is neutral. But tough votes like this could make more Democrats vulnerable.

A regional breakdown of the roll-call vote on Waxman-Markey shows why the bill, as written, would face a difficult road in the Senate. According to data compiled by carbon economists Matthew Kahn and Michael Cragg, the 12 states where per capita carbon emissions are highest have only 55 seats in the House, about an eighth of that chamber. From those states, 42 members, including 11 Democrats, voted against the bill. The same states have 24 Senate seats, nearly a quarter of that chamber. Half of those Senate seats are held by Democrats whose votes Majority Leader Harry Reid, D-Nev., would badly need. As if that weren't enough, remember that Democrats need 60 percent of the Senate but managed to muster only 50.3 percent of the House.

This article appeared in the Saturday, July 11, 2009 edition of National Journal.

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