But in his 80s, and eager to see his warnings about the perils of making war reach a wider audience than even his bestselling book, McNamara agreed to sit for hours of questioning by Morris. The film that emerged from the collaboration—The Fog of War—won the 2003 Academy Award for Best Documentary Feature. In my (admittedly biased) judgment, at least, the film succeeded in giving McNamara the opportunity to examine the calamity that Vietnam represented and explore how similar tragedies might be avoided. The movie continued McNamara’s efforts to revisit the decisions that led to the conflict, with this goal as expressed in the opening pages of In Retrospect:

We of the Kennedy and Johnson administrations who participated in the decisions on Vietnam acted according to what we thought were the principles and traditions of this nation. We made our decisions in light of those values. Yet we were wrong, terribly wrong. We owe it to future generations to explain why.

McNamara’s determination to leave a legacy that might somehow prevent a repeat of history—an American engagement in a war that would fail to achieve honorable objectives and a democratic denouement—will no doubt be in the back of many viewer’s minds as Morris’s newest film, The Unknown Known, rolls out in theaters (and, simultaneously, on-demand from cable outlets and iTunes). In his new movie on Rumsfeld, Morris’s approach is very much the same as it was with McNamara. His off-camera voice poses questions and, amid archival clips and original musical soundtracks, the subjects reveal personalities that are riveting in their differences.

The film on McNamara drew heavily from his experiences—reaching as far back as his time in service during World War II and the Cold War, especially the Cuban missile crisis, and exploring his outlook shaped by the long-term dangers of confronting the Soviet Union—to frame the lessons that he learned for avoiding future war. McNamara’s sense of responsibility was palpable in the film (as it was in his books), though he chose his words carefully, refusing to say why he did not speak out against the Vietnam War and declining to assess his successor’s policies. “You don’t know what I know about how inflammatory my words can appear,” he said, in a climactic exchange. “A lot of people misunderstand the war, misunderstand me. A lot of people think I’m a son of a bitch.”

By contrast, the thrust of Rumsfeld’s jousts with Morris are built around his stream of memos—he estimates there were 20,000 in his years at the Pentagon—and linguistic formulations, the most famous of February 4, 2002, in which he wrote, “There are knowns, known unknowns, and unknown unknowns. ... There are also unknown knowns: things you think you know that it turns out you did not.” Whereas McNamara is a man grappling with the consequences of his actions, Rumsfeld, as characterized by Morris, “is a man using language to obscure the world from himself as well as from others.”