Legislative. Carried out by the Environmental Protection Agency (EPA) and re-interpreted various times. It is the main federal law regulating air emissions from stationary and mobile sources, and authorises the EPA to set and enforce standards for air pollutants. In 2009, the EPA issued the Endangerment Finding, ruling that greenhouse gas emissions endanger public health and welfare and establishing the legal basis for the EPA to regulate GHGs under the Act. Thus, it underpins a wide range of federal climate regulations, including GHG vehicle emissions standards, power plant regulations, and controls on industrial pollution. In February 2026, the EPA under the Trump administration moved to revoke the Endangerment finding, with many of these regulations at risk of or already repealed.