Still, the fight over California’s pollution rules could have serious consequences for the state’s ambitious climate goals, as well as national implications.

Here’s what you need to know:

What has already happened?

As early as summer of last year, the Trump administration released a proposal that would freeze fuel-efficiency and emissions standards for cars that had been put in place by President Barack Obama. Revoking California’s special authority to set its own pollution rules were part of the plan.

Trump administration officials said the move would save lives by lowering barriers to getting drivers into newer, safer cars. (That conclusion clashed with an Obama administration analysis.)

[Read more about environmental rules being rolled back under President Trump.]

At the time, the plan was met by criticism not just from environmental groups and states like California, but also the auto industry, whose representatives have long said that the uncertainty over regulation would discourage investment and innovation.

Then, a couple of months ago, in July, four of the world’s largest automakers signed a deal with California siding with the state over the federal government, prompting surprise and outrage from the president.