Arlen SpecterThe big news today is Sen. Arlen Specter’s announcement that he’ll be switching parties from Republican to Democrat. For the best analysis of why he did it (basically, he was fated to lose the upcoming primary), see Eric Kleefeld at TPM. The boss man asked me to weigh in from Paris on what it might mean.

The short answer: on optics, on symbolism, on portent, it’s a big deal. On the prospects for energy and climate legislation in this Congress, it means very little.

On symbolism, Specter’s statement says it all:

Since my election in 1980, as part of the Reagan Big Tent, the Republican Party has moved far to the right. Last year, more than 200,000 Republicans in Pennsylvania changed their registration to become Democrats. I now find my political philosophy more in line with Democrats than Republicans.

This is only the latest and most potent symbol that the Republican Party no longer has room for moderates, that it is shrinking into itself and becoming ideologically pure, ideologically extreme, and increasingly distant from the American mainstream. Recent polling shows voters fleeing — only around 30% of voters now self-identify as Republicans, with close to 50% Dem. The party is now entirely dominated by douchebags that everyone hates.

Specter isn’t the only remaining Republican moderate that’s noticed:

“On the national level of the Republican Party, we haven’t certainly heard warm, encouraging words about how they view moderates, either you are with us or against us,” [Sen. Olympia] Snowe [R-Maine] said. She said national Republican leaders were not grasping that “political diversity makes a party stronger and ultimately we are heading to having the smallest political tent in history for any political party the way things are unfolding.”

Will Maine’s moderate Republican senators, Snowe and Susan Collins, follow Specter’s lead? That would be a big frakking deal!

Now, as for energy and climate legislation:

Dems now have a 60 vote majority in the Senate (at least once Franken’s finally seated), which is enough to overcome the now-routine Republican filibuster. But Specter has made clear that he’s not changing his positions and specifically that “I will not be an automatic 60th vote for cloture.”

So what are his positions on climate change? Roughly those of a conservative Democrat. He voted against the McCain-Lieberman climate bill twice and declined to vote for cloture for the Lieberman-Warner climate bill last  year. He said that the latter bill contained “very difficult standards which I, candidly, do not think are attainable.” As an alternative he has pushed a bill co-sponsored with Sen. Jeff Bingaman, the “Low-Carbon Economy Act,” which has weak targets, free permits, automatic off-ramps, and all the rest of the kinds of provisions that neuter a climate bill. (See Wonk Room for more on Specter’s green record.)

Given that the Waxman/Markey climate bill is considerably more ambitious than Lieberman-Warner — and likely will remain so even after being hashed over by the House’s conservative Dems — there is every likelihood that Specter, along with many other conservative Dems like Bayh and Nelson, will vote the bill down, or at least weaken it until it’s worthless.

In other words, he’ll do what he would have done anyway.

The more interesting possibility is the somewhat remote chance that Specter could face a primary challenge from the left and lose to a real Democrat, a reliable climate vote. But that is highly, highly unlikely. Dems will almost certainly have 60+ votes in the Senate after 2010 anyway, and for now they need to keep Specter happy.