According to Michael O'Brien of the Washington Monthly, on February 7, 1960, Frank Sinatra and Campbell were in Las Vegas, where Sinatra introduced her to John F. Kennedy, then a senator and presidential candidate. In her 1977 memoir, she said that she became one of JFK's mistresses for a period of about two years, frequently visiting him in the White House after he was elected president. Her account was supported by phone records and other documentation, although Kennedy staff and supporters attacked her veracity when she published her memoir. A few months later in 1960, Sinatra introduced Campbell to "Sam Flood", who was Sam Giancana, the leading figure in the Chicago Mafia. She also became involved with him and knew his associate John Roselli.