IT ALWAYS COMES BACK TO THE SENATE BLUE DOGS…. By some measures, today is something of a breakthrough moment for climate-change legislation. The House Energy and Commerce Committee will begin work today on a cap-and-trade bill shaped by Reps. Henry Waxman (D-Calif.) and Ed Markey (D-Mass.), a compromise measure that Joe Romm has called “a stunning legislative achievement.”

Paul Krugman noted that the measure, which has been endorsed by Al Gore, has come under fire from conservative global-warming deniers, and some environmental groups that have argued it compromises too much. Krugman argued, however, that it’s a big step in the right direction.

[T]he bill represents major action to limit climate change. As the Center for American Progress has pointed out, by 2020 the legislation would have the same effect on global warming as taking 500 million cars off the road. And by all accounts, this bill has a real chance of becoming law in the near future.

So opponents of the proposed legislation have to ask themselves whether they’re making the perfect the enemy of the good. I think they are.

After all the years of denial, after all the years of inaction, we finally have a chance to do something major about climate change. Waxman-Markey is imperfect, it’s disappointing in some respects, but it’s action we can take now. And the planet won’t wait.

The “disappointing” aspects of the bill are the result of watering the legislation down to garner support from less progressive Democrats. It worked: Rep. Rick Boucher (D-Va.), a key House centrist, endorsed the bill last week.

Does this point to a chance at real progress on addressing the climate crisis? It might, if it weren’t for the Blue Dogs in the Senate. Roll Call reports today that the House compromise has given the legislation some “momentum,” but “it still may not be enough to break the logjam in the Senate.”

…Senate Democratic aides said that while the House deal is encouraging, it’s not clear how lasting it will be or whether it can overcome the deep-seated concerns of a host of moderate Senators. […]

Another senior aide said Waxman’s “pragmatic approach … will be appreciated in the Senate” but cautioned that the deal is unlikely to fully satisfy Senate moderates who are looking to temper the bill even more.

“Rick Boucher does not equal Evan Bayh does not equal Debbie Stabenow,” the senior Senate Democratic aide said of the Democratic Senators from Indiana and Michigan, respectively. Bayh and Stabenow have expressed reservations about cap-and-trade provisions, which would cap emissions and allow industries to trade for pollution permits.

“There are a substantial number of moderate Democrats who are uneasy at best,” the knowledgeable Senate Democratic aide noted.

Remember, Boucher is from a coal-rich, conservative district in Southwestern Virginia, and he’s on board with the Waxman-Markey compromise. But senators like Bayh and Landrieu are “uneasy,” putting the future of the bill in doubt.

At a certain point, Bayh and the Blue Dogs will simply have to decide whether they have the stomach to govern. There are real crises in need of real solutions, and “centrist” Democrats seem reluctant to rise to the occasion.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.