It was fifteen years ago today that Timothy McVeigh killed 168 people by detonating an explosives-filled truck near the Alfred P. Murrah Federal Building in Oklahoma City in the nation's deadliest-ever homegrown terrorist attack. McVeigh was an anti-government extremist inspired by the 1993 raid on the Branch Davidian compound at Waco; he railed against taxes, gun control and federal interference in Americans' lives. Those who betray the Constitution, he wrote in a letter, "are domestic enemies and should and will be punished accordingly." After the attacks, McVeigh suggested that he acted for the "larger good" and said that even if...