The Trump administration just eliminated the landmark finding that has underpinned federal regulations on planet-heating pollution since 2009. For nearly the past two decades, the “endangerment finding” has allowed the Environmental Protection Agency (EPA) to craft rules limiting greenhouse gas emissions under the Clean Air Act. Rather than repealing those rules individually, the Trump administration can undermine them all at once by attacking the endangerment finding. Today, the EPA finalized its plans to overturn the endangerment finding as part of its attempts to overhaul tailpipe pollution standards. Congress would have to enact legislation to regulate greenhouse gas emissions again at the federal level.