A small group of conservative activists has worked for 16 years to stop all government efforts to fight climate change. Their efforts seem poised to pay off.

In the summer of 2022, Democrats in Congress were racing to pass the biggest climate law in the country's history and President Joseph R. Biden Jr. was declaring that global warming posed a "clear and present danger" to the United States.

Two of them, Russell T. Vought and Jeffrey B. Clark, were high-profile allies of Donald Trump. Mr. Vought, who has railed against "climate alarmism," and Mr. Clark, who has called climate rules a "Leninistic" plot to seize control of the economy, drafted executive orders for the next Republican president to dismantle climate initiatives.

The other two, Mandy Gunasekara and Jonathan Brightbill, were lesser-known conservative attorneys with long histories of fighting climate initiatives. Ms. Gunasekara, a onetime aide to the most vocal global warming denialist in the Senate, and Mr. Brightbill, who had argued in court against Obama-era climate regulations, collected an "arsenal of information" to chip away at the scientific consensus that the planet is warming, documents show.

"We are pretty close to total victory," said Myron Ebell, who helped the first Trump administration set up its operations at the E.P.A. and has been attacking climate science and policies for nearly three decades.

Mr. Ebell said that dozens of conservative activists, lawyers, scientists and others had worked for years to prepare the case against the endangerment finding. But he singled out Mr. Vought, Mr. Clark, Mr. Brightbill and Ms. Gunasekara as the ones who drafted detailed plans of attack that the second Trump administration has largely followed.

"No amount of outside public support would have done anything if there hadn't been those four people: Russ and Jeff and John and Mandy," he said.

Still, some conservative activists who insisted that the threat of climate change was overblown kept up the fight during the Biden years.

One of them was Ms. Gunasekara, who served as E.P.A. chief of staff during Mr. Trump's first term and wrote the E.P.A. chapter in Project 2025, the set of conservative policy recommendations for a second Trump term. Another was Mr. Brightbill, a partner at the law firm Winston & Strawn who had served in the Justice Department's environment division during the first Trump administration.

Ms. Gunasekara is known in Washington for handing a snowball to James M. Inhofe, then a Republican senator from Oklahoma and her boss, on a cold February day in 2015. Mr. Inhofe held up the snowball in the well of the Senate as evidence that the planet could not be warming dangerously.