The United States and Iran signed a landmark agreement aimed at ending the nearly four-month war. U.S. gas prices dropped below $4 for the first time since March. Federal authorities said the suspected ringleader in the UFC terror plot is an illegal immigrant from Mexico accused of helping plan a mass-casualty attack at the White House Freedom 250 event. Find out what investigators said the group discussed—including snipers and drones. The Supreme Court is drawing a new line on gun rights and drug use. In a unanimous decision, the justices rejected a federal firearms charge against a Texas man who used marijuana....