Bobby Kennedy for President, over its four-hour running time, uses its subject as a kind of microcosm for American politics itself. The first episode deals with John F. Kennedy’s presidency, which it uses to consider the tension between getting ahead and doing the right thing. Bobby, his brother’s campaign manager during JFK’s presidential run, had cut his teeth working with Senator Joseph McCarthy, a family friend, but quit when he grew disillusioned with the senator’s ruthless investigations of suspected communists. In the early days of the Kennedy administration, both brothers were slow to embrace the burgeoning civil-rights movement; Robert Kennedy, then attorney general, was publicly critical of the Freedom Riders. But he changed his mind when he “saw people suffering,” U.S. Rep. John Lewis argues in the series.

The second episode considers Kennedy’s campaign for U.S. Senate in 1964, while he was still reeling from the assassination of his brother. It was at this point, Porter suggests, that he started to engage more passionately with issues where he felt he could make a difference. Porter interviews former Kennedy aides and activists in his orbit, who recall his trips to rural communities assailed by poverty. Marian Wright Edelman, the founder of the Children’s Defense Fund, describes initially thinking that Kennedy was only making these visits to get some positive press coverage. But she was startled by his focus. “Robert Kennedy was not who I thought he would be,” Edelman says. “He was listening, and he was learning.”

What’s apparent throughout the film is how many of the problems Kennedy spoke up about during the 1960s continue to divide America today. In 1968, the year of Kennedy’s presidential run and assassination, the country seemed riven by violence. January saw the Tet Offensive in Vietnam, and subsequent protests raging at home. At the end of that month, the journalist Pete Hamill wrote a letter to Kennedy imploring him to run for president, which Hamill reads from in the series. “I don’t think we can afford five summers of blood,” Hamill had written. “If you won, the country might be saved.” In April, Martin Luther King Jr. was assassinated. Porter includes archival footage of Kennedy breaking the news to a largely black crowd in Indiana, and quoting Aeschylus. What the country needs most now, he tells them, isn’t more division and hatred, but “love and wisdom and compassion toward one another.”

Just a few months later, Kennedy himself was assassinated in the kitchen of the Ambassador Hotel in Los Angeles. Porter, who has an extraordinary amount of footage to work with, restages the event via photographs of a dying Kennedy lying in the arms of a busboy, Juan Romero. She interviews Romero, as well as Paul Schrade, one of Kennedy’s staff members who was also shot that day. Schrade’s efforts to uncover information that he says was withheld about Kennedy’s death occupy much of the final episode, which considers Sirhan Sirhan, the Jordanian national who shot Kennedy, and interviews Sirhan’s brother. It’s here that the documentary’s running time feels prolonged. There are certainly parallels to be drawn between current extremist movements in the U.S. and the wave of assassinations of political figures in the ’60s, but Kennedy himself is such a charismatic presence throughout that the series loses momentum after his death. The question of who might have killed him—and why—is obviously a compelling one. Still, Porter’s presentation of his life is more surprising, and somehow more riveting.