In a move signaling an intention to dismantle President Obama’s climate change and environmental legacy, President-elect Trump will nominate Scott Pruitt, the attorney general of the oil and gas intensive state of Oklahoma, to head the Environmental Protection Agency.

Pruitt has spent much of his energy as attorney general fighting against the agency he will now lead.

Pruit, who has written that the debate on climate change is “far from settled,” joined a coalition of state attorneys general in suing the agency’s Clean Power Plan, the principal Obama-era policy aimed at reducing the U.S.’s greenhouse gas emissions from the electricity sector. He has also sued, with fellow state attorneys general, over the EPA’s recently announced regulations trying to curtail the emissions of methane, a powerful greenhouse gas, from the oil and gas sector.

He has also taken on the administration in other areas, joining other Republican attorneys general in a lawsuit over Obama’s immigration policies.

An ally of the energy industry, Pruitt also came to the defense, along with fellow Alabama attorney general Luther Strange, of oil company ExxonMobil when it fell under investigation by attorneys general from more liberal states seeking information about whether the oil giant failed to disclose material information about climate change.

“We do not doubt the sincerity of the beliefs of our fellow attorneys general about climate change and the role human activity plays in it,” they wrote at the conservative publication National Review. “But we call upon them to press those beliefs through debate, not through governmental intimidation of those who disagree with them.”

In an interview with the Post in September, as a D.C. federal appeals court was preparing to hear arguments over the Clean Power Plan, Pruitt detailed why he had remained a leading opponent of the EPA’s efforts to curb carbon emissions by regulating power plants.

“What concerns the states is the process, the procedures, the authority that the EPA is exerting that we think is entirely inconsistent with its constitutional and statutory authority,” he said at the time.

Agencies such as the EPA, he said, should not be trying to “pinch hit” for Congress.

“This is a unique approach by EPA, whether they want to acknowledge it or not,” he said of the provisions of the Clean Air Act the agency had relied upon to write new regulations.”The overreach is the statutes do no permit [EPA officials] to act in the way they are. They tend to have this approach that the end justifies the means …They tend to justify it by saying this big issue, this is an important issue.”

But he added that’s where Congress should have authority, not EPA. ” This is something from a constitutional and statutory perspective that causes great concern.”

Environmental groups reacted with alarm Wednesday at the nomination.

“Scott Pruitt has a record of attacking the environmental protections that EPA is charged with enforcing. He has built his political career by trying to undermine EPA’s mission of environmental protection,” said Fred Krupp, the president of the Environmental Defense Fund. “Our country needs – and deserves – an EPA Administrator who is guided by science, who respects America’s environmental laws, and who values protecting the health and safety of all Americans ahead of the lobbying agenda of special interests.”

Rhea Suh, president of the Natural Resources Defense Council, said that “over the past five years, Pruitt has used his position as Oklahoma’s top prosecutor to sue the EPA in a series of attempts to deny Americans the benefits of reducing mercury, arsenic, and other toxins from the air we breathe; cutting smog that can cause asthma attacks; and protecting our wetlands and streams.”

In 2014, the New York Times reported that Pruitt wrote a letter alleging that the agency overestimated air pollution from natural gas drilling, but that the letter was written by lawyers for Devon Energy, one of the state’s largest oil and gas companies.

But industry representatives expressed satisfaction on Wednesday. “The office he headed was present and accounted for in the battle to keep EPA faithful to its statutory authority and respectful of the role of the states in our system of cooperative federalism,” said Scott Segal, head of the policy group at the lobbying and legal firm Bracewell. “Given that we are almost two decades overdue for an overhaul of the Clean Air Act, there is interest on both sides of the aisle to look at that statute.”

The state’s natural gas output accounts for 10 percent of the nation’s overall. For the week ended Oct. 28, there were 73 drilling rigs in operation in the state.

The nomination suggests an extraordinarily tough road ahead for the Clean Power Plan, president Obama’s signature climate policy. However, the precise fate of the regulation most immediately turns on the U.S. Court of Appeals for the D.C. Circuit, which has not yet ruled in the lawsuit brought by Pruitt and his fellow attorneys general against the agency Pruitt is now named to lead.

Dismantling the regulation if it survives the courts would not be simple, because the agency has already finalized it – meaning that it would have to go through a public review and comment process.

However, interestingly, many of the Clean Power Plan’s signature objectives appear to have been already realized long before it came into effect. The U.S. is already burning less coal and more natural gas. In 2030, the EPA said in its final Clean Power Plan rule, coal would be reduced to providing 27 percent of the U.S.’s electricity, with natural gas at 33 percent. Yet this very year, according to the U.S. Energy Information Administration, natural gas will provide 34 percent of U.S. electricity, and coal 30 percent.