Of the three Kennedy brothers -- John, Robert and Edward -- who ascended to the national political stage in the 1950s and '60s, it was arguably the middle brother, Bobby, who best embodied the enormous contradictions at play within that famed (and, it sometimes seems, cursed) American family.
There was, for example, RFK's fraught relationship with liberals -- and with American liberalism in general. (As the author and historian Sean Wilentz once wrote, while his liberal doubters saw Kennedy as ruthless and occasionally unprincipled, RFK "regarded his liberal critics as hopeless, sanctimonious losers who put purity above political realism, and who seemed to think that sure-fire defeat was inherently noble.")
Then there was his relationship with Lyndon Johnson -- a man who, according to virtually everyone who knew both men, hated Bobby Kennedy with an intensity matched only by RFK's loathing for his bother's successor as president.
But Kennedy also had an intellectual heft that makes most present-day American politicians seem sadly trifling by comparison. (Is there a sitting U.S. senator or representative whom one can picture quoting Herodotus or Sophocles, from memory, as Kennedy so often did?)
Finally, like his brothers -- especially John -- Robert Kennedy was able to powerfully connect with crowds in a way that most politicians can only envy, and there were certainly people who saw greatness in him and in his future.
"He is one of the half-dozen men in the country today qualified for top political leadership," one of Lyndon Johnson's advisers told LIFE magazine in 1964, when Kennedy was on the cusp of running for the Senate. "He really cares about right and wrong. He cares about people."
Here, on what would have been Robert Kennedy's 89th birthday (he was born Nov. 20, 1925, in Brookline, Mass.), LIFE.com shares photos -- most of which never ran in LIFE magazine -- of Kennedy and his extended and immediate family in 1964. The pictures, by LIFE's George Silk, capture a man who, as Robert Ajemian wrote in the magazine's July 3, 1964, issue, "had shouldered massive burdens" in the six months since his brother John was gunned down in Dallas the previous November.
A major preoccupation of Bob Kennedy's in the past six months [Ajemian wrote] has been his family -- and now it includes his brother's children, Caroline, who is 6, and John, who is 3. Jackie Kennedy brings them out almost every day to their uncle's home, Hickory Hill, five miles outside Washington. Bob and [his wife] Ethel spend as much time with them as with their own brood of eight."
Four months after LIFE ran its cover story, Robert Kennedy was elected as the Democratic U.S. Senator from New York. He served until June 1968, when he was assassinated by a gunman named Sirhan Sirhan, while campaigning in Los Angeles for his party's presidential nomination. Robert Kennedy was 42 when he was killed -- four years younger than John Kennedy was when his life was taken.