In the first year of his presidency, Donald Trump has withdrawn the United States from the Paris climate agreement, scrapped the Clean Power Plan that sought to cut greenhouse gas emissions from power generation, pushed to open up new areas of the Arctic and Gulf of Mexico to oil drilling, and blocked government climate scientists from presenting at professional conferences.

But for fossil fuel advocates, deregulation crusaders and climate skeptics who gathered in Houston last week for the Heartland Institute’s America First Energy Conference, Trump has still not gone far enough.

What Heartland, a free-market think tank based in Chicago, really wants is to revoke the “endangerment finding,” which since 2009 has served as the basis for climate policies and regulations.

That includes the Clean Power Plan, the main plank of Barack Obama’s climate program, which would have brought the United States within reach of meeting its commitments to the Paris agreement.

So far, however, Trump and Environmental Protection Agency Administrator Scott Pruitt have not tried to overturn the endangerment finding. And that is a mistake, according to several people at the Heartland conference.

However, Trump and Pruitt are coming under growing pressure to try to scrap the finding from a number of figures who have played an influential role in the administration’s thinking about climate change — including two members of the president’s transition team who spoke at the Heartland conference: Steve Milloy and David Schnare.

“The endangerment finding is the root of all global warming evil at the EPA, and we’re trying to figure out here what is the best way to get that thing reconsidered and undone,” Milloy,  an attorney and long-time opponent of the EPA who runs the website, told the Heartland conference.

“It’s not really clear that the administration views this with the same urgency that we do,” he added.

The endangerment finding states that emissions of greenhouse gases such as carbon dioxide and methane from burning fossil fuels count as air pollutants under the Clean Air Act and endanger public health and welfare. It provides the legal justification for the EPA to regulate these harmful gases.

The finding has been repeatedly upheld by the U.S. Court of Appeals for the District of Columbia Circuit and other jurisdictions. Recent scientific studies, including the National Climate Assessment report released earlier this month, have also helped reinforce the finding.

Michael Gerrard, a director of the Sabin Center for Climate Change Law at Columbia University and who was not at the conference, said there is little chance of overturning the finding.

“Those who favor its repeal probably see it as their Hail Mary play — the odds are low, but if they win, they win big,” Gerrard said.

But that did not deter the speakers at the Heartland conference, including Milloy and Schnare.

“The goal here is not to change the policy but to correct the science,” said Richard B. Belzer, an independent consultant on regulatory economics and a fellow at the free-market R Street Institute think tank.

Belzer has also previously worked with the Competitive Enterprise Institute, which, like the Heartland Institute, was once merely a right-wing outlier. The organizations’ libertarian positions put them in the fringe of U.S. politics — only 1 in 10 Americans consider themselves libertarians and know what the term means, according to Pew Research Center survey — yet they have effectively become policy brain trusts of the Trump administration.

Schnare, former director of the Free Market Environmental Law Clinic, called on Trump and Pruitt to coordinate their approach toward the endangerment finding.

“You’re only going to be successful if you get the EPA and [White House’s] Office of Science and Technology Policy working together,” Schnare said. 

However, Trump has yet to appoint a White House science adviser.

Schnare argued that to remove the endangerment finding, each line of evidence supporting it needs to be challenged.

Other speakers went on to attack the science behind the finding.

Harry MacDougald, an attorney at an Atlanta law firm who previously worked with the Competitive Enterprise Institute to challenge the endangerment finding, disputed the mainstream scientific consensus that global temperatures have exceeded natural variation and that oceans have become more acidic due to climate change. 

The Competitive Enterprise Institute filed a petition to the EPA to reconsider the endangerment finding earlier this year while making similar claims.

Even if climate scientists are right, MacDougald argued, climate regulations would  impose a “colossal expenditure.”

That argument — about the costs of cutting emissions — could be gaining traction in Pruitt’s EPA, said Holly Doremus, an environmental law professor at the University of California at Berkeley who was not a participant at the conference. “The EPA is sympathetic to that argument now in a way that it wasn’t in 2009,” she said.

However, Gerrard argued that, for the time being at least, the endangerment finding is on firm ground and that as a result the EPA is legally required to cut greenhouse gas emissions that cause climate change. “I think that Pruitt is being advised that trying to revoke the endangerment finding would be a clear legal loser,” he said.