Democrats, progressives, and Trump unenthusiasts had girded themselves to be outraged by the candidates Donald Trump would choose to fill his Cabinet, and, so far, his nominees have not disappointed. A retired neurosurgeon who has likened anti-segregation efforts to communist oppression will be in charge of Housing and Urban Development. A former Goldman Sachs banker will lead the Treasury Department. A billionaire who wants to dismantle the public-school system has been nominated as Secretary of Education. And most recently, wrestling executive and longtime Trump supporter Linda McMahon was rewarded with the Small Business Administration. But the announcement that Scott Pruitt would head up the Environmental Protection Administration—an agency that the Oklahoma attorney general has spent most of his career attempting to destroy—has rightly touched the rawest nerve, setting off what could be a drawn-out and contentious Senate confirmation fight as Democrats vow to oppose his appointment.

“We’re certainly going to draw a line in the sand,” Hawaii senator Brian Schatz told The Hill. “This is the worst-case scenario when it comes to clean air and clean water, to nominate a climate denier to the agency charged with protecting our natural resources.” Senator Bernie Sanders, who sits with Schatz on the Environment and Public Works committee, said he will “vigorously” oppose Pruitt, whom he described not only as a “climate denier” but “someone who has worked closely with the fossil fuel industry to make this country more dependent, not less, on fossil fuels.” Connecticut senator Richard Blumenthal also told The Hill “there will be a fight” over Pruitt’s nomination.

Safeguarding both the agency and President Barack Obama’s legacy on the environment is a top priority for Democrats, who see climate change as an existential threat. And while Republicans hold a slim majority in the Senate, Democrats hope they can sway some of their colleagues across the aisle or, at the very least, make plenty of noise during Pruitt’s confirmation hearing. “The E.P.A. is our cop on the beat, protecting the American people and our environment from harmful pollution, hazardous waste and the impacts of climate change,” Massachusetts senator Ed Markey told Bloomberg. “He has dedicated years of his career to rolling back the bedrock laws and rules that protect our water and our air.”

While Trump’s other Cabinet appointments range from unqualified to ideologically opposed to the departments they would lead, Pruitt stands out for his very public hatred of the E.P.A. In recent years, he’s led a coalition of conservative state attorneys general, along with oil and energy companies, against Obama’s climate-change agenda, suing the E.P.A. in federal court over the regulation of carbon-emissions. He’s also taken his grievances beyond climate change, suing to overturn regulations and protections covering clean air, ozone pollution, and mercury. He himself bragged on his official bio that he is “a leading advocate against the EPA’s activist agenda,” a position that Trump seemed to endorse in a statement confirming Pruitt’s nomination Thursday. “For too long, the Environmental Protection Agency has spent taxpayer dollars on an out-of-control anti-energy agenda that has destroyed millions of jobs, while also undermining our incredible farmers and many other businesses and industries at every turn,” Trump said.

Pruitt’s nomination was roundly criticized beyond Capitol Hill, too. “This is an aggressively bad choice,” The New York Times wrote in an op-ed, “a poke in the eye to a long history of bipartisan cooperation on environmental issues, to a nation that has come to depend on the agency for healthy air and drinkable water, and to 195 countries that agreed in Paris last year to reduce their emissions of climate-changing greenhouse gases in the belief that the United States would show the way.” Several environmental groups and activists echoed the Times, with billionaire hedge-fund manager and noted climate activist Tom Steyer describing Pruitt as “about the worst thing [Trump] could be doing for the environment and the American people.”

Although it only takes a simple majority vote for the Senate to confirm a Cabinet appointment, and they can no longer be filibustered, Democrats and their independent allies have vowed to deny the nomination at all costs. “We are totally mobilizing on this one,” Schatz told Bloomberg, adding that he expected Pruitt’s confirmation “will be extremely difficult.”