On the eve of Donald Trump’s inauguration as president, U.S. Sen. Angus King said he will oppose the Republican leader’s choice to head the Environmental Protection Agency.

“I just can’t, in good conscience, as somebody who’s taken seriously environmental protection all my life, approve the appointment of someone who is so manifestly opposed to the mission of the agency,” King told Maine Public Radio on Thursday.

Trump’s pick, Oklahoma Attorney General Scott Pruitt, has been a target for environmentalists who wonder about his ability to lead an agency he’s sued repeatedly.

Maine’s other senator, Republican Susan Collins, hasn’t decided yet what she will do with Pruitt’s nomination.

Collins’ spokeswoman, Annie Clark, said the senator met with Pruitt this month and “discussed with him many important environmental issues about which she cares deeply. This weekend she will begin to review his testimony from his confirmation hearing yesterday.”

A group of 75 scientists and medical professionals signed a letter to the senators this week, organized by the Union of Concerned Scientists,  said Pruitt’s “past actions subjugating science and public health to the benefit of private industry make him an unacceptable choice to run the EPA, an agency whose mission is to protect our air and water, and the health of all Americans.”

They said Collins and King should “stand up for public health in Maine.”

A coalition of environmental groups in the state also wrote to both senators Thursday to plead with them to block Pruitt.
 
“Maine needs an EPA Administrator who will work to protect the clean air and clean water that are so vital to our economy, health, and quality of life. Mr. Pruitt, however, is hostile toward EPA’s mission and is determined to weaken the nation’s most important environmental laws,” said the letter signed by groups ranging from the Maine Clammers Association to The Wilderness Society Maine.
 
The groups said they represent more than 75,000 Mainers who oppose Pruitt, who testified before the Senate Environment and Public Works Committee on Wednesday.
 
Pruitt already has the support of one Democrat in the Senate, West Virginia’s Joe Manchin. The New York Times said he is expected to receive the backing of all 51 Senate Republicans as well. A simple majority is needed to approve the nomination.