Robert McNamara, the former secretary of defense and an architect of the Vietnam War, said it all could have been different if McGeorge Bundy, President Lyndon Johnson's national security adviser, had not resigned from the White House in early 1966.

"I believe if McGeorge Bundy had stayed in the government . . . he and I together could have prevented what happened in Vietnam," McNamara said in August 2007, less than two years before his death. "He and I together could have done what I couldn't do alone, which was force the president to an open debate on these critical issues."

In their final interviews, McNamara and Bundy dissected America's failures in managing the Vietnam War. In haunting, mournful tones, they blamed not only Johnson and senior...