Next week Mr. Tribe is to deliver oral arguments for Peabody in the first federal court case about Mr. Obama’s climate change rules. Mr. Tribe argues in a brief for the case that in requiring states to cut carbon emissions, thus to change their energy supply from fossil fuels to renewable sources, the E.P.A. is asserting executive power far beyond its lawful authority under the Clean Air Act. At a House hearing last month, Mr. Tribe likened the climate change policies of Mr. Obama to “burning the Constitution.”

To Republicans who oppose Mr. Obama’s climate change agenda, Mr. Tribe is a celebrated convert. “When I saw the brief, I thought, this is dazzling,” said Michael McKenna, a Washington energy lobbyist. “And the fact that it was written by a guy on the other side made it even better.”

Senator Mitch McConnell of Kentucky, the Republican majority leader, has frequently cited Mr. Tribe’s brief in speeches and letters as part of a campaign urging governors not to comply with the climate change rules. “As iconic left-leaning law professor Laurence Tribe put it, the administration’s effort goes ‘far beyond its lawful authority,’ ” Mr. McConnell wrote in an op-ed article in The Lexington Herald-Leader last month.

To many Democrats and professors at Harvard, Mr. Tribe is a traitor. “The administration’s climate rule is far from perfect, but sweeping assertions of unconstitutionality are baseless,” Jody Freeman, director of the environmental law program at Harvard Law School, and Richard Lazarus, an expert in environmental law who has argued over a dozen cases before the Supreme Court, wrote in a rebuttal to Mr. Tribe’s brief on the Harvard Law School website. “Were Professor Tribe’s name not attached to them, no one would take them seriously.”

Mr. Tribe’s legal claims, they concluded, are “ridiculous.”

Mr. Tribe dismissed the criticism and said that his brief and comments reflect his views as a constitutional scholar, not as a paid advocate for the coal company. “I’m not for sale,” he said. “I’ll say what I believe.”