The national rollback, which will be finalized later this year, has already been denounced by environmental groups, consumer advocates, and public-health organizations. But automakers and even the acting EPA administrator, Andrew Wheeler, also remain skeptical of the proposal. As I wrote in June, the car industry is happy to see the fuel-efficiency rules weakened. It would just prefer for the policy change to be a little quieter, a little subtler, a little less Trumpian.

President Trump is said to have been involved in choosing the final policy proposal, though—so maybe that was never an option.

There’s little doubt that the rollback will have long-term consequences for the climate. The transportation sector, which includes cars and trucks (and also planes), now emits more heat-trapping gas than any other part of the U.S. economy. The proposed freeze will not press carmakers to produce more efficient vehicles, at exactly the time when manufacturing cleaner and more efficient vehicles is one of the country’s most pressing environmental needs.

Yet it’s not exactly new for a Republican administration to battle stricter fuel-efficiency rules. President George W. Bush did it too, for a time, until a spike in gas prices and a Democratic-controlled Congress forced him to act in 2007. What’s most notable is that—by attacking California’s Zero Emission Vehicle program—the Trump administration is also attacking the state’s ability to regulate not just greenhouse gases, but conventional air pollution.

There are big differences between these two types of pollution—both scientifically and politically. Greenhouses gases are at their most harmful when they accumulate in Earth’s atmosphere and trap heat, causing the planet to warm. They’re only dangerous, in other words, when dispersed through Earth’s atmosphere. But conventional air pollution can trigger immediate and local health problems. Ozone, for instance, exacerbates asthma and other respiratory problems. Particulate matter can cause early deaths and diabetes.

Atmospheric scientists have long recognized that, when it comes to conventional air pollution, California has a more difficult challenge than everyone else. Not only does the state contain some of the country’s largest car-dependent cities, but the unique geography of the Los Angeles Basin—which pairs insistent sea breezes to the west with imposing mountains in the east—can essentially trap smog in place for days at a time.

Even today, the EPA says that two of California’s regions—including the Los Angeles Basin—are so polluted with ozone that they are in “extreme nonattainment” with federal standards, the worst possible designation.

Congress has also recognized that California has a tough task. When they passed the Clean Air Act, lawmakers carved out a special waiver process for the state, allowing it to set higher standards than the federal government. Any other state could then choose to accept these standards. Today, 13 states use these stricter pollution rules, including New York, Pennsylvania, and New Mexico.