It’s official: The Trump Administration has killed the legal and scientific basis for US action on greenhouse gas emissions.

During a press briefing on Thursday, President Trump and Environmental Protection Agency (EPA) Administrator Lee Zeldin Office has partnered the reversal of the agency’s “endangerment finding”, which ruled in 2009 that global warming gases such as carbon dioxide are dangerous to human health and well-being. This landmark decision gave the US the power to regulate greenhouse gas emissions for nearly two decades.

Basically, if American climate policy is a house of cards, the Trump administration just pulled the card that kept the whole thing alive.

Environmentalists have been preparing it for months. Zeldin first announced the EPA’s bid to withdraw the finding while speaking at an Indiana car dealer in July. In its proposal, the agency argued that the measure would save Americans $54 billion annually by removing all greenhouse gas standards for vehicles and engines, including Biden’s electric car mandate.

Of course, that rationale was the central focus of Thursday’s briefing. Trump called the move “the single largest act of deregulation in American history” and warned of the risk of “a disastrous Obama-era policy that has severely damaged the American auto industry and significantly raised prices for American consumers.”

“It’s a big deal,” Zeldin said. “This action will save American taxpayers more than $1.3 trillion.” Yet the EPA’s own draft impact analysis estimated that eliminating risk-taking could cost consumers more, not less—potentially up to $350 billion in additional fuel costs each year. And that doesn’t include the costs of public health consequences and environmental damage from greenhouse gas pollution.

Why is this important?

The Clean Air Act NEEDS the EPA to regulate any air pollutant that harms the health or welfare of the public. In 2007, the Supreme Court Controls that greenhouse gases are subject to this mandate. Two years ago, the search for danger determined that current and projected atmospheric concentrations of six key greenhouse gases “threaten public health and well-being for present and future generations.”

A concurrently issued “cause or contribution finding” focuses on vehicles and machinery as the main source of dangerous greenhouse gas emissions. These determinations serve as the legal basis for the EPA to control global warming pollution, and over the years, the scientific evidence supporting them has only grown.

Over the past seven months, scientists, climate advocates, environmental policy experts, and former EPA leaders have warned that the repeal will have dire consequences for America’s health, well-being, and climate. While the EPA’s proposal directly targets vehicle emissions, the agency is also willing to roll back regulations for new and existing fossil fuel-fired power plants and oil and gas facilities. According to Harvard Lawcanceling the search for risk will almost certainly encourage efforts.

The Trump administration withdrew the risk finding on the grounds that it lacked legal authority under the Clean Air Act to regulate greenhouse gas emissions. If the courts endorse that view going forward, future administrations would also be prevented from regulating global-warming pollution under the Act, Harvard Law said.

“Abandoning all efforts to address climate change is not in the best interest of anyone but the fossil fuel industry, which has made trillions of dollars in profits over the past 50 years and has shown that if left unchecked, it will continue to profit at any cost, even if that destroys the American way of life,” said Shannon Baker-Branstetter, senior director of domestic climate at the Center for American Progress, statement after Zeldin’s announcement in July.

The repeal is expected to face legal backlash from environmental organizations and coalitions in Democratic-led states. “This cynical and devastating action by the Trump EPA will not go forward without a fight,” said Manish Bapna, president and CEO of the Natural Resources Defense Council. SAYS in a statement following Thursday’s announcement. “We’ll see them in court—and we’ll win.”