Since Christmas Eve in 1865, membership in the Ku Klux Klan ignited and multiplied three separate times, in each instance enacting brutal violence and terror — but the Klan’s power never held for long. Though only 2 dozen Klan groups exist today, its continued importance lies in a far more elusive and sinister legacy. Watch CNN’s Original Series “The People v. The Klan” on Sunday, April 18 starting at 9 p.m. ET/PT.