Violent white supremacy is part of rising domestic terrorism in the U.S., and this essay highlights steps political leaders can and should take to stop it. In 2015 a white supremacist with a handgun walked into a historic African-American church in Charleston, S.C., and murdered nine worshippers. Domestic terrorism, as defined by federal law, consists of criminal acts on U.S. soil that are dangerous to human life and are intended to coerce and intimidate a civilian population. A bill now in Congress, the Domestic Terrorism Prevention Act, would remedy this omission. It authorizes the creation of offices in three agencies—Homeland Security, the Justice Department and the FBI—to monitor, investigate and prosecute cases of domestic terrorism.