“Whether he intended it or not, Tribe has been weaponized by the Republican Party in an orchestrated takedown of the president’s climate plan,” said one former administration official.

Thomas Reynolds, a spokesman for the E.P.A., reacted to Mr. Tribe’s brief by saying that agency officials remained confident in the legal arguments behind the regulations. “We have a recent record of court wins, proving our work is grounded in a sound understanding of the law,” Mr. Reynolds said in an email.

Mr. Tribe said he could not help it if Republicans embraced his arguments. He has never met or spoken with Mr. McConnell, he said, and disagreed with Mr. McConnell’s advice to states to ignore the rules, since states could face steep fines for failure to comply with the rules while they are still in place.

“I’m worried about being used to encourage the states to take risks that may be unwise,” Mr. Tribe said.

While Mr. Tribe is one of the nation’s foremost experts on constitutional law, and has argued some Supreme Court cases related to environmental law, he said he has never specialized in the Clean Air Act. Although Mr. Obama has been speaking publicly since 2013 of his use of the Clean Air Act to carry out climate change regulations, Mr. Tribe said that he was unaware of the regulations until last fall.

Mr. Tribe said he was retained by the company as an independent expert to provide his own views and not to repeat the company’s. But the public comment is signed by both Mr. Tribe and Peabody officials.

“That a leading scholar of constitutional matters has identical views as officials of a coal company — that his constitutional views are the same as the views that best promote his client — there’s something odd there,” said Richard L. Revesz, director of the Institute for Policy Integrity at the New York University School of Law.