Nothing brings together diverse groups like a common threat. And governors in environmentally progressive states are getting used to banding together against the Bush administration.

Now they’ve done it again, to protest the “cynical” effort by the Bush Department of Transportation to take away the right of California to set tougher greenhouse gas standards for cars (and the right of other states to adopt the California standards).

The latest assault on states’ rights came in the fine print of a proposal this week by the DOT to put into place tougher CAFE standards required by last year’s energy act. On page 387 of that proposal, DOT slipped in the killer language: “any state regulation regulating tailpipe carbon dioxide emissions from automobiles is expressly pre-empted.”

This language, first flagged publicly by California Attorney General Jerry Brown, brought a fierce response yesterday by 12 governors led by California’s Arnold Schwarzenegger.

In a letter to congressional leaders, the governors (also from Ariz., Conn., Md., Mass., N.J., N.M., N.Y., Ore., Pa., Vt., and Wash.) assailed what they described as a “cynical attempt” by the car company-owned transportation agency “to unilaterally re-write the Clean Air Act and claim authority over greenhouse gas emissions.”

Many readers may recall that the car companies tried — and failed — to insert similar language in the energy bill. The governors were quick to point out that the proposal would “usurp congressional authority and patently subvert the clear intent of Congress.”

In a separate letter to the president, the governors threatened a suit unless the transportation department drops the provision.

Get ready to go to court. The Bush administration obviously made a deal with the car companies persuading them to swallow tougher CAFE standards in return for a pledge to block California and the states.