The EPA's 2009 Greenhouse Gas Endangerment Finding has been the legal foundation for U.S. climate regulation under the Clean Air Act for over a decade. In February, the Trump administration repealed it. That move puts the future of federal climate policy in question. Professor Alejandro Camacho explains what the endangerment finding did and why it mattered for policies ranging from vehicle emissions to power plant rules. Drawing on his new book, he also puts this moment in context: showing how earlier waves of environmental policymaking took shape in the 1960s and '70s, and why today's approach is marked by polarization, legal battles, and uncertainty.

For more on this topic:

• Check out the book Camacho coauthored, Lessons for a Warming Planet: A Vital History of US Environmental Law

• Read his commentary in Legal Planet, The Trump Administration is Squandering Our Natural Heritage

• Read his op-ed in The Hill, Donald Trump's record-breaking race to wreck the planet