Even as President Trump pulls back on regulations governing car emissions, part of a broader policy of overturning environmental protections enacted by the Obama administration, California is determinedly headed in the opposite direction with stricter rules it alone is authorized to enact.

During a visit to Detroit last month, Trump halted the imposition of standards that would cut car emissions almost in half by 2025, including greenhouse gases that are responsible for global warming. The administration instead will reopen a review of the standards at the request of the major automakers, giving them the chance to argue that the rules should be eased.

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Attempts to undercut the standards will prompt drawn-out litigation from states such as California or New York, Sivas predicted. To reverse an earlier decision, the EPA will have to go through the same series of elaborate steps that were taken to put the rules into place.

“They can’t just say, ‘Oh yeah, well forget that,'” Sivas said.

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“Given all that it will be tough for EPA to say we’re going to rescind your waiver,” Sivas said. “So I think California has the upper hand in that fight if it comes down to that.”

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If the Trump administration were to try to withdraw the waiver, Sivas thought California would win in court.

“It’s pretty clear under the statue that the deference goes to California not to the EPA on whether the waiver is appropriate,” she said. “The Congress wrote the statute that way.”