Jeff BingamanNew Mexico Sen. Jeff BingamanBig news today: Sen. Jeff Bingaman (D-N.M.), chair of the Energy and Natural Resources Committee, is retiring. He won’t run for reelection in 2012. All political pundits are required by law to write something about What This Means, so here goes.

First, it means Senate Dems are not very optimistic about their chances in 2012. Jim Webb (Va.) and Kent Conrad (N.D.) are also declining to run for reelection. Janet Napolitano recently announced she won’t run for the open Arizona seat. The basic problem is that 21 Senate Dems are up for reelection in 2012 and fully a third of those races are in states that either went McCain in 2008 or lurched rightward in 2010. Republicans, meanwhile, are defending just 12 seats and are likely to have a financial advantage. It’s just a grim map for Dems and the smart money is on the Senate going Republican in 2012. Being in the minority is no fun.

Second, in the particular case of New Mexico, it’s probably not worth Dems panicking. If Obama is going to win reelection, he’ll win the state, and it’s a “lean Dem,” so a good Senate candidate has solid chance of winning.

Third and most importantly, Bingaman’s loss is a serious blow to greens. He is one of the few members of the Senate who truly understands U.S. energy policy, one of the few who has credibility across the aisle, and one of the few adept and effective enough to actually get stuff done. The rest of the green leadership in the Senate is either bumbling and ineffective (Barbara Boxer, John Kerry) or too junior to have the juice to make things happen (Jeff Merkley, Tom Udall).

Don’t get me wrong: I’ve had my frustrations with Bingaman. He’s not as ambitious as I’d like. He largely stayed on the sidelines during the climate-bill debate, grumbling about how there aren’t enough votes, which sent a signal to other moderates to keep their distance. But in retrospect, there’s a case to be made that Bingaman was right: Dems might have had more success if they’d put forward a modest clean energy bill and let him lead it through his committee.

Regardless, this is a loss of a deep reservoir of clean energy expertise in an institution where such expertise is in woefully short supply. Hard as it is to believe, the Senate may be even worse on this issue after Bingaman is gone.