A mini-imbroglio has broken out in the blogosphere over the Sierra Club’s decision to formally endorse Senator Lincoln Chafee (R-R.I.). A similar dust-up took place late last year over NARAL’s decision to endorse Chafee. Both endorsements were largely deplored by the progressive blogs, with a few dissenters.

I’m going to argue for what might seem a slightly odd position: NARAL made a terrible decision; the Sierra Club made a good one.

Start with this premise: For a variety of structural and historical reasons, party discipline has increased sharply in American politics over the last few decades. We more and more resemble a parliamentary system. So the relevant questions here have less to do with Chafee’s own positions or votes than with party dynamics — specifically, Republican party dynamics.

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On both abortion and the environment, Chafee is an exception to the prevailing Republican position. But Republican party dynamics are vastly different on the two issues.

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On abortion, battle lines are drawn. It’s a fight to the death. No partisan on either side will ever be persuaded to change sides, so at this point it’s just a matter of who can muster the political power to enforce their position. Party lines are sharp: The Republican Party will always be home for anti-abortion single-issue voters, and the Democratic Party will always be the inverse (though it’s occasionally gone wobbly). There is nothing Chafee could do — as a Senator or as a symbol — to change the Republican Party on this question.

In short, endorsing Chafee means endorsing the anti-abortion party, irrespective of his personal views.

But the environmental dynamic is different. During the ’80s and ’90s, it came close to becoming a strictly partisan issue, but environmental issues do not sit comfortably in that niche. There are more and more signs that concern over the environment — public lands, the energy crisis, global warming — is crossing party lines (see Christina’s excellent piece on the subject). The corporate forces that govern the Republican Party have tried their best to make environmentalism synonymous with fuzzy-headed socialism, but in the long term they were always destined to fail. It is a time of great ferment and upheaval in the Republican Party on this particular issue. Party discipline is breaking down.

In other words, the iron is hot. The time is ripe. Whatever. This is a time when the Republican Party’s resistance to environmental sanity can be changed.

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For this reason, environmental champions among the (R) ranks need, now more than ever, to be vocally and publicly supported. Chafee has proven instrumentally effective at blocking some of Bush’s environmental madness, but just as much he serves an important symbolic role. Republicans in Congress, and out in the hinterlands, need to be shown that a) it’s safe to be a Republican environmentalist, and b) environmental organizations will welcome them. If they’ll drop the partisan warfare, the Sierra Club will too.

Environmentalism is not yet a party-transcending issue, not totally, but it could become one. The Sierra Club is trying to help that process along. Time will tell if they succeed, but I don’t begrudge them the attempt.

(From the Sierra Club, Carl Pope and Paul Rauber defend the decision; over on MoJo blog, Brad Plumer does too.)