The Trump administration moved to lower nationwide vehicle fuel efficiency rules today by arguing that dirtier cars will be safer. The administration is also trying to take away California’s power to set its own greenhouse gas emissions standards and zero-emission vehicle program, which are initiatives that many other states around the country have followed for years.

It’s a move that fulfills two of President Donald Trump’s common goals: undercutting Barack Obama’s policies and weakening environmental regulations. The decision, which has been in the works for well over a year, has already sparked a firestorm of reactions from state prosecutors, environmental organizations, industry players, and former EPA staff members. What’s more, the fight over California’s role in steering the country’s environmental policy sets up what could be one of the most consequential legal battles the Trump administration has taken on to date.

Taking aim at a key Obama climate policy

The rules this administration is trying to roll back were announced in 2009 and put in place in 2012. They set standards all the way out to 2025 that would force automakers’ fleets to eventually reach an average fuel economy of 54.5 miles per gallon. Automakers, the government, and states agreed to the rules, which were part of President Obama’s broader efforts to fight climate change (since fuel efficiency is so closely tied to emissions).

The rules as written were on track to reduce greenhouse gas emissions by hundreds of millions of metric tons and cut oil consumption by over 1 billion barrels — all while saving customers billions of dollars at the pump. Since the program stretched so far out into the future, the EPA under Obama checked in on automakers’ progress in 2016. It determined then that “the record clearly establishes” the standards were “practical and feasible,” and found automakers were already “over-complying” ahead of schedule.

Trump’s EPA quickly got to work by reopening that review in early 2017. And in April this year, it announced that it would propose new rules, which is what happened this week.

The EPA and Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) released what’s known as a “proposed rule” on Thursday. It still has to go through a public comment period, and a final rule isn’t expected until after that. The NHTSA and the EPA will hold three public hearings on the proposal, too — one in Washington, DC, another in “the Detroit, MI area,” and a third “in the Los Angeles, CA area.” Dates for the hearings have not been set.

The new proposal, which the EPA co-developed with the NHTSA, essentially calls for a freeze of the standards at the level they are currently scheduled to reach in 2020. That means automakers’ fleets would only have to meet an average fuel economy of 43.7 miles per gallon by 2020, and they would no longer need to improve beyond that.

Rolling back emissions standards is “potentially more damaging than the repeal of the Clean Power Plan”

“This particular rollback of one of the centerpieces of the Obama administration’s climate policy is actually potentially more damaging than the repeal of the Clean Power Plan,” Ann Carlson, the Shirley Shapiro professor of environmental law at UCLA, tells The Verge. “The reason for that is because transportation sector emissions have been rising as opposed to declining.”

The electricity sector in the US, Carlson says, is seeing declines in emissions across the board because of the country’s shift toward natural gas and an increased reliance on renewable power. “But in the transportation sector, we have forces going in the opposite direction,” she says. “We have low gas prices. We have, because of the economic improvement, drivers driving more, so increases in vehicle miles traveled. And the result of that is that it’s much harder to get the transportation emissions curve bending in the correct direction without strong government intervention.”

The EPA and NHTSA say that lowering these targets will save lives, and they provide a few potentially flawed reasons to support that claim in the proposal. First and foremost, they argue, “unreasonable fuel economy and CO2 Standards” lead to “increased vehicle prices [that] keep consumers in older, dirtier, and less safe vehicles.” The agencies then point to a February 2018 Kelley Blue Book analysis that shows the “average new vehicle transaction price” recently passed $36,000, which represents an increase of more than $3,000 since 2014. But they fail to note that Kelley Blue Book attributes this increase to the shift in consumer preference to (typically dirtier) trucks and SUVs, not as a result of compliance with strict emissions standards.

If new cars continue to get more expensive, the agencies’ argument continues, consumers are more likely to hold on to the older cars they already own or buy older used cars. And since overall vehicle safety typically increases with each model year, this means more people are likely to die if they are widely discouraged from buying new cars. Therefore, the EPA and NHTSA estimate that freezing the fuel efficiency standards at 2020 levels could lead to a $2,700 reduction in the upfront cost of a new car, and those savings could, in turn, prevent 12,700 deaths over the next 10 years.

In addition to this argument, the EPA and NHTSA say that dirtier cars will be safer than more fuel-efficient ones for two other reasons. More fuel-efficient cars could cause people to drive more, they say, which would, in turn, increase the number of accidents on the road. And since one way that automakers achieve greater fuel efficiency is to make cars lighter, the two agencies argue that drivers will be less vulnerable in heavier, dirtier cars.

Leading automakers have met with Trump in private, but are mostly mum in public

Leading automakers have seen sales boom in the decade since the 2008 recession, even while adjusting their future fleets to include more hybrid and electric vehicles as part of an effort to meet the Obama-era goals. The biggest ones have repeatedly met in private with President Trump about the national emissions standards and reportedly lobbied against a freeze. But they have said little of substance about the potential rollback in public.

General Motors said Thursday it “remain[s] committed to a future of zero crashes, zero emissions, and zero congestion,” but declined to comment on any of the specifics. Fiat Chrysler said the proposed rule “includes a range of options, and we will carefully evaluate how each aligns with FCA’s goals of continuous improvement in vehicle efficiency,” but it also declined to comment on specifics. A representative for Ford did not respond to a request for comment.

Environmental agencies, industry groups, states, and even Arnold Schwarzenegger, however, have already pushed back strongly against the Trump administration’s move.

“The federal government’s own data shows that when managed properly for vehicle footprints, light-weighting and fuel economy rules don’t undermine highway safety,” says Robbie Diamond, president and CEO of nonpartisan energy policy group Securing America’s Future Energy. Heidi Brock, president and CEO of the Aluminum Association’s Transportation Group, agrees. In a statement, she says data used in the EPA and NHTSA’s own proposed rule undercuts the argument about lighter cars being more dangerous.

Threats to take the EPA and NHTSA to court over the decision are already flying. “The Trump administration is handing automakers years of uncertainty and litigation,” says Ben Longstreth, the deputy director of the Natural Resources Defense Council’s federal policy, climate, and clean energy program. “We would prefer a different path, but if the administration finalizes this terrible proposal, we’ll have to see them in court.”

A coalition of 20 state attorneys general, including California AG Xavier Becerra and New York AG Barbara Underwood, said the attempted rollback will cost consumers “hundreds of billions of dollars” and it puts “the health of our children, seniors, and all communities at risk.” The group threatened a lawsuit once the rule is finalized; Becerra is already leading 17 states in a lawsuit over the decision to revisit the standards in the first place.

Acting EPA head Andrew Wheeler reportedly pushed the White House to ease off the rollback

“At first glance, this proposal completely misrepresents costs and savings. It also relies on bizarre assumptions about consumer behavior to make its case on safety,” California Air Resources Board (CARB) head Mary D. Nichols said in a statement. “CARB will examine all 978 pages of fine print to figure out how the Administration can possibly justify its absurd conclusion that weakening standards to allow dirtier, less efficient vehicles will actually save lives and money.”

Some of the pushback over the decision has even reportedly come from inside — and even atop — the EPA. Acting EPA administrator Andrew Wheeler reportedly “sharply questioned the auto fatality numbers” that the standards rollback is partly built on, according to The New York Times. Wheeler feared “that if they are proven faulty, that will undermine the legal case for the rollback,” sources told the paper.

Additionally, The Washington Post recently obtained part of an internal presentation from the EPA’s Office of Transportation and Air Quality, that warned the proposed rulemaking contained “a wide range of errors, use of outdated data, and unsupported assumptions.”

On a call with reporters on Thursday, the NHTSA’s acting administrator Heidi King and the EPA’s assistant administrator Bill Wehrum did not deny those claims when they were asked whether the proposed data was sound.

The EPA’s assistant administrator admitted this proposal will weaken the protections of public health and the environment

“The great detailed analytical information, assumptions, data files, and even the models themselves are posted on our website today for public review,” King said. “We are open to, and we, in fact, encourage, rigorous review of all the quantitative information used in this rulemaking.”

“This is complicated stuff. Eventually, we just have to call balls and strikes, put our analysis out there,” Wehrum said. “What really matters is when we get to the final rule stage, and what matters then is to have the very best analysis we can.”

Wehrum also admitted that freezing the standards would make the country’s citizens more vulnerable to negative health effects as a result of climate change, but he argued that the calculations the EPA and NHTSA have made about the number of lives they think will be saved is worth that trade-off.

“The very most important thing about this rule is, yeah, if we lock in the 2020 standards, we’re not getting as much emissions reduction as we otherwise would have, and that translates into incrementally less protection of health and the environment,” he said. “But balanced against that, our current analysis shows, we get substantial improvement in vehicle highway safety. And when you monetize the improvement in highway safety and compare that to the monetized value of the health and environmental protection from emissions control, the highway safety numbers swamp the environmental numbers.”

“This has to go down in the books as one of the dumbest [decisions] ever.”

Massachusetts Attorney General Maura Healey warned the Trump administration on a call with reporters to “gear up for a big fight” over the proposal. “We’ve seen a lot of stupid, harmful decisions by the Trump administration and the EPA,” she said. “But this has to go down in the books as one of the dumbest ever, when you think about the harm to the air quality and the health of our children and communities, the harm to the consumers at the pump, and frankly, the harm to an auto industry that has already taken steps in light of the Obama administration’s rules to innovate, to make more efficient cars, and a product that they would be able to sell here and across the world.”

Trump v. California

While a large focus of the proposed rulemaking is on the national targets, the EPA and NHTSA are also attempting to revoke the Clean Air Act waiver that grants California the power to set its own greenhouse gas emissions standards and run a zero-emission vehicle program.

Because California was already setting its own aggressive environmental standards before the Clean Air Act was signed into law in 1970, the state was allowed within the framework of the legislation to obtain waivers to the federal program. That special authority is what has allowed the state to be so progressive with its environmental rules over the last few decades, and many other states now follow its lead, including a dozen that have adopted its vehicle emissions standards.

The Trump administration has sparred with California on a number of issues since the election, but this could be the biggest legal fight yet between the two sides. “The federal government tried back in the Bush years to use this argument to evade California’s historical role in setting vehicle standards to protect its air quality,” Stanley Young, a spokesperson for CARB recently told The Verge. “But it’s a tired legal argument that was litigated and lost twice in Federal District Courts, and is related to an important decision by the Supreme Court [Massachusetts v. EPA] that declared greenhouse gases an air pollutant,” he said.

“the Trump administration is walking on very thin ice.”

The EPA and NHTSA argue in the proposal that since all states experience effects from climate change, California isn’t unique, and therefore it doesn’t have “compelling and extraordinary circumstances” to set its own greenhouse gas emissions standards. A big question going forward will be whether the federal government has the authority to revoke waivers already granted for these specific standards and programs.

“Under the Clean Air Act, there is no provision for revoking waivers, so the Trump administration is walking on very thin ice,” Margo Oge, the former director of the EPA’s Office of Transportation and Air Quality under President Obama, said on a call with reporters. “There is no way that this awful approach is going to succeed in court.”

Oge, who helped design the original standards that were put in place in 2012, called the reversal attempt “politically motivated” and said this was a very sad day for her personally.

“Hundreds of engineers [worked] around the clock with California’s engineers. We went to every company in the US, we had companies coming from Asia and from Europe, to negotiate those standards. People missed birthday parties, they missed holidays. Forget about vacations. I personally missed my youngest daughter’s engagement party because we were working so hard to do something so extraordinary,” she said. “What happened in 2012 was the most extraordinary thing that I have done in my career of 32 years at EPA.”

“But more important, this is a sad day for our country, the citizens, and our planet as a whole,” she added.