Minutes before the televised debates between Vice President Richard Nixon and Sen. John F. Kennedy in 1960, a Nixon aide asked Bobby Kennedy how his candidate looked. Eying Nixon’s five o’clock shadow and pallid skin, Bobby proclaimed, “Terrific. I wouldn’t change a thing,” turned to his older brother and whispered “Kick him in the balls.”

The story, which may be apocryphal, captures one side of Robert F. Kennedy, the ruthless hypocritical political manager. The other Bobby, embraced by admirers in the 1960s (and now), is a hardheaded softhearted idealist, a fierce advocate of racial justice, a champion of the poor, and a foe of the war in Vietnam, the only man who could have united — and transformed – the country.

In “Bobby Kennedy: The Making of a Liberal Icon,” journalist Larry Tye, the author of biographies about Satchel Paige and Superman, draws on hundreds of interviews with RFK’s family, friends, colleagues and critics and recently released documents to provide an evocative in-depth portrait of the most complicated Kennedy. Enchanted by Kennedy since he was in high school, Mr. Tye sets the historical context for Bobby’s evolution, which occurred in fits and starts, “from cold warrior to hot-blooded liberal.” More passionate, more provocative and more accessible than his older brother, Mr. Tye argues, Robert Kennedy “could become this nation’s high priest of reconciliation because he had once been the keeper of our darkest secrets.”

Mr. Tye’s account of Kennedy’s early career is insightful, nuanced, fair and balanced. A member of Sen. Joseph McCarthy’s Subcommittee on Investigations in the 1950s, Bobby picked up bad habits, Mr. Tye writes, such as believing the United States was overrun by communists, and good ones, “like investigating his adversaries with rigor and care.” Robert Kennedy, who divided the world into friends and fiends, Mr. Tye notes, maintained a relationship with McCarthy after he was censured by the Senate.

As chief counsel of the Senate Rackets Committee, Mr. Tye reminds us, Kennedy went after Jimmy Hoffa, head of the International Brotherhood of Teamsters, relentlessly and self-righteously, ridiculing witnesses who invoked their constitutional rights against self-incrimination. Convinced that the corrupt Hoffa posed a threat to labor-management relations, Kennedy allowed his idealism to trump his objectivity. Ironically, his vendetta, which continued when he became attorney general in his brother’s administration, made Hoffa a hero to 1.5 million Teamsters while reinforcing Kennedy’s reputation as “vindictive, ambitious, frosty and ruthless.”

When he turns to the five years between John Kennedy’s assassination and Bobby’s death on the night of his victory in the California presidential primary in 1968, Mr. Tye becomes more sentimental and celebratory. Like Don Quixote, the hero of “Man of La Mancha,” a musical he saw three times, Bobby, Mr. Tye suggests, tended to dream and tilt at windmills. As a U.S. Senator from New York and a candidate for president, Mr. Tye claims, without much evidence (apart from Bobby’s soaring rhetoric), Kennedy was willing to experiment with radical solutions and use political capital. “He had skipped straight to revolutionary,” taking on as his mission uniting working-class whites and poor blacks in a political coalition committed “to change the country and the planet.”

Bobby’s “hard-as-nails shell,” the author maintains, “protected a deep, reassuring tenderness.” Deeply sympathetic to Kennedy for making forgotten and neglected Americans his primary constituents, Mr. Tye chooses to end his biography with a moving — and myth-making — tribute to Robert Kennedy, the person. “There will be no more football with Daddy, no more swimming with him,” 13-year-old David Kennedy wrote to his mother. “But he was the best father their [sic] ever was and I would rather have him for a father for the length of time I did than any other father for a million years.”

Glenn C. Altschuler is the Thomas and Dorothy Litwin Professor of American Studies at Cornell University.

First Published: July 3, 2016, 4:00 a.m.