The Trump administration on Friday launched an all-out assault on California over automotive mileage rules, telling state officials that only the federal government has the power to regulate greenhouse gas emissions and fuel economy.

The assault began with the Justice Department opening an antitrust investigation into a deal between California and four automakers for tougher pollution and related mileage requirements than those sought by President Donald Trump. Then, two federal agencies told the state it has no authority to regulate greenhouse gas emissions.

Janet McCabe, former acting assistant EPA administrator for air and radiation, said California has the legal power through the Clean Air Act to regulate auto pollutants that include greenhouse gases. "Their job is to reduce emissions," she said. "They're not regulating fuel economy, they're regulating emissions," said McCabe, now a professor at Indiana University's McKinney School of Law.