The legal battle raises novel questions about the Clean Air Act, a landmark piece of legislation signed into law in 1963, that will be tested for the first time in this case. The case is expected to go all the way to the Supreme Court.

"I would say it's going to be a very strong case but not necessarily a slam dunk," said Todd Aagard, a former Justice Department attorney who worked in the agency's environment and natural resources division.

But legal experts say that California, which formally filed suit alongside 23 other states on Friday, has a strong case that the administration's move is unlawful. And, they say, there is virtually no way in which the legal fight is over before the 2020 presidential election, meaning voters will also get a say in the matter.

The Department of Transportation and the Environmental Protection Agency announced on Thursday that they were doing away with the 2013 carveout, which was one of President Barack Obama's signature measures to contain climate change.

The Trump administration has a steep hill to climb before it can revoke a waiver that allows California to set separate rules that govern auto emissions.

Chief among the new questions: Can a waiver ever be revoked? To date, despite California receiving roughly 100 waivers for its vehicle standards, it has never happened. The Clean Air Act itself does not address the matter.

The Trump administration will make the case that the law must provide the ability to revoke a waiver because it provides the ability to grant one, said Richard Revesz, a leading scholar of environmental and regulatory law and the director of the nonpartisan Institute for Policy Integrity at the New York University Law School.

"That argument works sometimes, but it doesn't work other times. For example, if the president issues a pardon for someone convicted of a crime, and a subsequent president thinks that's a bad idea, it can't be rescinded," Revesz said.

Revesz said that there are reasons to believe that a waiver can't be revoked in this particular case. For one, he said, California has obligations to meet certain federal environmental goals, and its plan to meet those goals is premised on the waiver. In addition, California has a strong interest in protecting the health and safety of its citizens.

"These reliance interests are important in the legal analysis, and California has very strong reliance interests," Revesz said. "The federal government has never even attempted or raised the possibility that rescinding a granted waiver could be done, and the general assumption is that it couldn't be done."

If a court determines that a waiver can be revoked, the question becomes under what circumstances an administration is allowed to do so.

In that case, the standards are likely to be drawn from the rules that govern when a waiver can be denied in the first place.

The EPA can deny a waiver if California's rules are less "protective of public health and welfare" than the federal rules, or if the state does not need it to meet "compelling and extraordinary" circumstances.

If those are determined to be the standards for revoking a waiver, then California will likely win, according to Michael Gerrard, a professor at Columbia Law School and the former chair of the American Bar Association's 10,000-member section on environment, energy and resources.

"Here, California can show that climate change is an extraordinary threat to the state. They don't have to show that it's uniquely a threat to California, just that they are affected," Gerrard said.

Gerrard said that the Trump administration will make the argument that it is important for there to be uniform federal standards. But he noted that, at the moment, the federal rules are the same as California's rules, despite attempts by the Trump administration to roll them back. In addition, 13 states and the District of Columbia have voluntarily signed on to California's standards.

"We have a uniform rule at the moment," he said. "It's the Trump administration that is trying to change the standard."

Gerrard said that the Trump administration will also argue that California's rules are impossible to meet. But that argument falls flat, he said, pointing out that automakers Ford, Volkswagen, BMW and Honda already agreed voluntarily to hit California's standards.

In a statement, a spokesperson for the EPA said that its rule "makes clear that California only has the ability to obtain a waiver for local effects of local pollution."

"But California cannot misuse that authority to set national fuel economy standards and attempt to control national greenhouse gas emissions standards. We are confident we are correctly applying the law and will prevail in the courts," the spokesperson said.