Fifty years ago, a group of Democratic and Republican senators spent months working together in Washington, D.C. to tackle a danger they all agreed was harming Americans’ health and lives. Huddled in committee rooms for hours on end, they listened to one another’s ideas, traded jokes across party lines and, in the end, produced a bill that won unanimous Senate approval and passed the House of Representatives with just one “no” vote.

The Clean Air Act, signed by President Richard Nixon on December 31, 1970, would become one of modern America’s most consequential laws. Translated into real-world rules by the newly established Environmental Protection Agency, the act has since reduced air pollution in the United States by 70 percent—even as