U.S. Marines are besieged at Khe Sanh and the Viet Cong launch the Tet offensive, the turning point in the Vietnam War. Meanwhile, the 1968 presidential election begins to take shape – Senator Eugene McCarthy dares to challenge the sitting president of his own party, Lyndon Johnson, while LBJ's greatest political rival, Senator Robert Kennedy, eyes his own entry into the race. Republican Richard Nixon begins his political comeback attempt with another presidential run, as controversial independent candidate George Wallace mounts a populist campaign. Rev. Martin Luther King, Jr. travels to Memphis in support of a local sanitation worker's strike. On the last day of March, President Johnson stuns the world with a surprise announcement that will change the course of history.