But wait — can’t California just make its own rules?

So what about those federal waivers California has to make its own rules, including a waiver that allows California to run aspects of its Advanced Clean Cars program?

Trump revoked California’s waiver to set its own tailpipe-emissions standards on Sept. 18, tweeting that his decision would make cars cheaper and safer and lead to more jobs. His long-expected announcement prompted denunciations from state leaders and presaged a drawn-out legal battle.

“See you in court,” Gov. Gavin Newsom tweeted in response, calling the federal decision “a continuation of a political vendetta.”

California’s air board is confident of its legal standing, in part, state officials say, because the federal agency has failed to make a scientific or technical case for the waiver decision. 

“Their work’s been bad. Their facts are bad,” said Craig Segall, assistant chief counsel for the California Air Resources Board, referring to the EPA’s analysis, which has been widely criticized. Anything can happen in litigation, he acknowledged, but “we’ve got the better of the argument, and it helps to have facts on your side.” 

On Sept. 20, California and 22 other states sued the National Highway Traffic Safety Administration, arguing that the administration exceeded its authority, made its decision without adequate justification and violated federal environmental law.

The state’s Advanced Clean Cars program sets limits on greenhouse gases and air pollutants in the exhaust from passenger vehicles. The program also requires automakers to serve up an escalating percentage of zero-emission vehicles to California’s car buyers.

California’s clean-air enforcers say getting more clean cars on the road will be key to curbing smog and meeting the state’s goal to cut greenhouse gases by another 40 percent. Trump’s rollbacks are expected to take California even farther from that target — increasing California’s greenhouse gas pollution by the equivalent of 12 million metric tons of carbon dioxide in 2030 alone, according to data from the air board.