For many years, CA had its own emissions standards, and auto manufacturers responded by making 49-state-equipped cars and CA-equipped cars. Of course, they could have (and I suspect, in some cases, did) respond by selling the cleaner CA cars everywhere. But, for the most part at least, the mfrs. knew consumers in the other 49 states would not be happy driving the slower and/or less-efficient CA-equipped cars, especially if the competition was selling faster, more-efficient cars.
That said, I believe individual states should be free to impose whatever emissions standards they wish on new, used, imported, or whatever cars they want at the peril of their voters. (For example,) Let North Dakota impose a hodge-podge of emissions standards, and see how many auto mfrs. simply decide not to sell cars to North Dakotans. Or, see how happy North Dakotans are in paying 20% more than South Dakotans for the same model.
Yes and California knows it is the biggest car market in the country. Did you catch that pointless piece of data saying that if california went to all zero emmision cars it would only lower world co2 levels by 1 percent? California's crazy laws invented the 10 billion dollar per year wind industry.