Washington (CNN) Senate Democrats are digging in their heels against President-elect Donald Trump's choice to helm the EPA -- Oklahoma Attorney General Scott Pruitt.

"This is a four-alarm fire. We are going to do everything we can to stop his nomination," said Sen. Brian Schatz of Hawaii.

"This is a full-fledged environmental emergency, and we have a person who's not just a climate denier, but a professional climate denier," Schatz said on a call organized by the League of Conservation Voters. "This is going to be a litmus test for every member of the Senate who claims not to be a denier."

Pruitt, the Oklahoma attorney general, has denied climate scientists' conclusion that human activity is warming the earth and has made his name through legal battles against the EPA over its regulations of power plants.

Pruitt also used state stationery and signed his name to letters that were drafted by fossil fuel industry lobbyists, The New York Times reported . Those letters, which were critical of federal environmental regulations, were sent to federal officials at the EPA, the Interior Department and the Office of Management and Budget.

The chief connection between Trump and Pruitt is Harold Hamm -- a billionaire energy executive who is a Trump energy adviser and co-chaired Pruitt's re-election campaign in 2013.

Sen. Tim Kaine of Virginia, the 2016 Democratic vice presidential nominee, said he fears Pruitt's installation at the helm of an agency where "virtually every decision they make is a decision that's based on science."

"If someone does not accept basic climate science, what other science don't they accept? So I'm very, very troubled by that," Kaine said.

Trump's Republican allies have said they see Pruitt's battles with the EPA as the reason he's ideal for the job.

"As a fellow fierce critic of the EPA, I know he's going to roll back the regulations that have been an overreach," Rep. Chris Collins, R-New York, said on CNN's "New Day" Thursday. "I look at Attorney General Pruitt as someone who understands the balance. The EPA is out of balance. They've gone to the extreme."

In a statement announcing Pruitt's nomination, Trump himself said Pruitt would reverse EPA policies.

"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. As my EPA administrator, Scott Pruitt, the highly respected attorney general from the state of Oklahoma, will reverse this trend and restore the EPA's essential mission of keeping our air and our water clean and safe," Trump said.

Even if Pruitt doesn't win the votes of Democratic senators in red states whose seats are up for re-election in 2018 -- including West Virginia's Joe Manchin, North Dakota's Heidi Heitkamp, Indiana's Joe Donnelly and Montana's Jon Tester -- the party still won't have enough votes to stop Pruitt's nomination on its own.

Democratic-backed changes to filibuster rules lowered the threshold to stop debate and force votes on presidential nominees from 60 votes to 51.

That means majority Republicans can push Pruitt and other Trump nominees through on their own.

So Democrats are attempting to heap pressure on Republicans who embrace climate science to break with their party's President-elect.

Republican senators who have voted for climate change bills in the past or who accept climate science, said Sen. Sheldon Whitehouse, D-Rhode Island, should oppose Pruitt.

"We have enough votes to prevent him from going forward if they'll stick with us," he said.

He also said corporations that have long based public relations campaigns on combating climate change should oppose Pruitt.

"If not, we will end up with an EPA that has been corrupted by the fossil fuels industry," Whitehouse said.

Democrats also pointed to the Times' report that Pruitt had signed his name to fossil fuel lobbyists' drafts of letters critical of the Obama administration's environmental regulations.

"I think that we should be prepared to talk about this not just as a matter of bad climate policy, but as a matter of corruption of government," he said on the League of Conservation Voters' call. "When you take a government agency whose primary present responsibility is to deal with the climate crisis and you turn it over to someone who has spent his entire life in service to the regulated industry, that satisfies virtually every definition of corruption of government, and that should be a theme of our efforts against him."

Sen. Jeff Merkley, D-Oregon, sounded a similar theme, saying Pruitt had been "caught red-handed putting arguments from fossil fuel lobbyists on his letterhead."

Pruitt's top target is likely to be power plant regulations that Republicans have long decried as onerous for energy companies, damaging to states where coal mining is an important industry and costly to consumers.

Beyond that, though, he might not have time over four years to change much, said Austin Whitman, the director of regulatory affairs for FirstFuel Software, which provides utilities information on customer energy use.

The process of developing and implementing new EPA regulations takes four to eight years, he said. "To build a coal plant, to build a pipeline, to build an LNG station can take years or decades. ... What happens in one to four years can only have a modest impact on that," Whitman said.

Advances in green energy industries, including solar power and wind farms, as well as local or state-level energy efficiency policies, has also spurred growth in those industries in typically Republican states.

So GOP lawmakers, he said, might not empower Pruitt to go beyond unraveling the Obama administration's power plant regulations.

"The EPA can't change the legislation -- you really would need Congress to step in and do that," he said.