The Trump administration has set in motion a potentially huge legal battle between the federal government and California.

Let's backtrack.

For decades, California has had the right to set its own limits on air pollution that comes from cars and trucks.

The state was granted this special right after facing some serious air pollution problems in the 1960s.

Those limits, typically, have been stricter than the standard set by the federal government.

And so, many other states across the country choose to opt in to California's standards.

The Trump administration, meanwhile, wants to change that.

On Wednesday, President Trump tweeted that he's revoking California's power to set its own standards.

The Environmental Protection Agency and the Transportation Department confirmed that move with a formal announcement Thursday morning.

It's a move that reflects a broader approach by the Trump administration to roll back Obama-era climate policies.

It may spark a legal battle that highlights the complicated relationship between federal law and states' rights.

It also raises questions about how climate policy is put in place, about how much a president can do on environmental regulation without passing laws through Congress,

and whether we're just stuck in a circle of setting and rolling back emission standards as administrations change.

This is Ken, he do that, a podcast that explores the powers and limitations of the American presidency.

I'm Alice Michaels.

Juliet Alperin is the Washington Post's National Affairs correspondent who's spent significant time reporting about environmental policy.

I asked her why fuel emission standards exist and what they're intended to do.

They are designed to tackle a couple of things, first and foremost, climate change.

The idea is the transportation sector now ranks as the biggest source of greenhouse gas emissions in the United States,

and tailpipe emissions are the largest portion of that.

The idea is from this point forward, for example, our power plants are already getting cleaner,

but if you really want to tackle climate change, you've got to deal with cars and trucks.

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