Laurence Tribe is arguably the nation’s foremost liberal legal scholar.

The longtime Harvard Law School professor – whose former students include President Barack Obama and Supreme Court justices John Roberts and Elena Kagan – notes that he taught the nation’s first environmental law class, nearly a half-century ago.

He also stated – in a recent email to the Atlantic’s David A. Graham – that he shares the Obama administration’s “attitude toward climate change and the urgency of meaningful action on that front.”

Tribe appeared Thursday before the U.S. Court of Appeals for the District of Columbia in a case challenging the constitutionality of the administration’s so-called Clean Power Plan, which mandates Draconian reductions in carbon emissions by the nation’s coal-fired power plants.

But – to the dismay of the Obama administration and its allies in the environmental community – Tribe’s presentation came not in defense of the Clean Power Plan but on behalf of Peabody Energy, the nation’s largest publicly held coal company, a party to the litigation (along with Murray Energy, the nation’s largest closely held coal company and more than a dozen states).

“Tribe sells his soul to Big Coal,” decried David Roberts, a writer for Grist, an online magazine billed as “‘The Daily Show’ of the environment.” Tribe is “destroying his reputation as one of the most important and thoughtful constitutional scholars in this country,” blogged Ann Carlson, a UCLA environmental law professor.

Tribe is unfazed by such besmirchment of his good name and reputation. “I’m not for sale,” he said. “I’ll say what I believe.”

What he believes is that the Environmental Protection Agency is doing an end run around the Clean Air Act in its zeal to implement Obama’s Clean Power Plan. In so doing, the agency is “asserting executive power far beyond its lawful authority,” Tribe contended.

Indeed, Tribe told the House energy and power subcommittee last month that rules devised by EPA would command every state by next year to develop a package of laws approved by the agency “requiring coal-fired to shut down or reduce operations, consumers and businesses to use less electricity and pay more for it, and utilities to shift from coal to other energy sources.”

Simply put, it would entail “a total overhaul of each (s)tate’s way of life.”

The problem, said Tribe, in an essay published in December by the Wall Street Journal, is that “EPA, like every other administrative agency, is constitutionally forbidden to exercise powers Congress never delegated to it in the first place.”

Yet, he continued, “EPA is acting as though it has the legislative authority anyway to re-engineer the nation’s electric generating system and power grid. It does not.”

Adding weight to Tribe’s conclusion is not only his stature as one of America’s foremost constitutional scholars, but also because he has previously argued in support of Obama’s executive authority to tweak the Affordable Care Act and to effectively suspend U.S. immigration law.

But Obama’s Clean Power Plan goes too far, Tribe told the New York Times. “I’m sure he’s motivated by a deep concern for climate change,” he said, adding that the president “believes he is following the Constitution as he understands it.”

Nevertheless, said Tribe, “I don’t take responsibility for the views of former students that I think are misguided.”

EPA is attempting “an unconstitutional trifecta,” he maintained. The regulatory agency is “usurping the prerogatives of the states, Congress and the federal courts – all at once.”

Obama’s former law professor continues to share the president’s belief that climate change is a clear and present danger to the planet. Indeed, he wrote, in the Wall Street Journal, “As a father and grandfather, I want to leave the Earth in better shape than when I arrived.”

But not by having the EPA make a mockery of the separation of powers. “Burning the Constitution should not become a part of our national energy policy,” said Tribe.