Traffic on the I-405 in Los Angeles. Eric Beteille / Flickr
By Nicholas Bryner and Meredith Hankins
Editor's note: On April 2, U.S. Environmental Protection Agency (EPA) Administrator Scott Pruitt announced that the Trump administration plans to revise tailpipe emissions standards negotiated by the Obama administration for motor vehicles built between 2022 and 2025, saying the standards were set "too high." Pruitt also said the EPA was re-examining California's historic ability to adopt standards that are more ambitious than the federal government's. Legal scholars Nicholas Bryner and Meredith Hankins explain why California has this authority—and what may happen if the EPA tries to curb it.