Why is this a problem? First of all, automakers already stated they simply can not meet the previously proposed standards. Secondly, the rest of the states in the union would be forced to acknowledge CARB's decision. That means even if you do not live in California CARB would still be able to push your state around.
Imagine for a moment a new car coming out with a lot of horsepower that is very efficient and meets EPA standards but does not meet CARB standards. Effectively, there would be two sets of emission standards in the USA but the CARB standards could force that automaker to abandon selling the car in the United States or even worse not bother producing it.
Want to know what is truly troubling? Arizona, Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Washington, and the District of Columbia all decided to agree to CARB's standards. That means many of you are not exempt from California's eco-nazis even if you do not live in California.
CARB gets away with setting federal standards as it pre-dates the EPA and a waiver under the Federal Clean Air Act means their emission standards must be recognized by other states.
What will happen? Who knows. The Trump administration froze EPA grants to CARB hitting them where it hurts. The Trump administration also cut funding to the EPA. The Obama administration on their way out rushed approval of new EPA standards that align with CARB prior to Trump taking office.
CARB blames the automakers:
Thanks a lot California.