His tenure is best known for its advocacy for the civil rights movement , the fight against organized crime and the Mafia , and involvement in U.S. foreign policy related to Cuba . After his brother 's assassination , he remained in office in the Johnson Administration for several months . He left to run for the United States Senate from New York in 1964 and defeated Republican incumbent Kenneth Keating . In office , Kennedy opposed racial discrimination and U.S. involvement in the Vietnam War . He was an advocate for issues related to human rights and social justice and formed relationships with Martin Luther King Jr. and Cesar Chavez
brother 's assassination
Assassination of John F. Kennedy
Robert F. Kennedy