[Bob Woodward is an associate editor of The Washington Post and the author of 14 books, most recently "The War Within: A Secret White House History, 2006-2008." Gordon M. Goldstein is the author of "Lessons in Disaster: McGeorge Bundy and the Path to War in Vietnam."]

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 military leaders for a dysfunctional decision-making process, but also themselves. The interviews provide a singular look into what went wrong -- as the two men saw it decades later, with the benefits and burdens of hindsight -- at a time when President Obama and his national security team engage in intense deliberations over another complex, distant conflict, this time in Afghanistan and Pakistan.

For a wartime president and his top advisers, "there ought to be anguish," McNamara concluded, because there "are no easy answers."

'A Man Who Didn't Want to Listen'

In his last extended interview, on Aug. 7, 2007, McNamara offered harsh views of Johnson as commander in chief. "I felt that I owed the president my best judgment, whether it agreed with his or not," he said. "The question in my mind was not so much whether I owed that to him; the question was how to present it effectively to a man who didn't want to listen."

Johnson, in McNamara's view, "was more afraid of the right than the left. And he was afraid that if he did anything to in any way appear to appease the North Vietnamese, he would be severely criticized by the right wing of American politics. Therefore he didn't do it."

In a final series of interviews before his death in 1996, Bundy also described how Johnson's short-term political concerns trumped grand strategy for Vietnam. "LBJ isn't deeply concerned about . . . who governs South Vietnam -- he's deeply concerned with what the average American voter is going to think about how he did in the ballgame of the Cold War," Bundy said. "The great Cold War Championship gets played in the largest stadium in the United States, and he, Lyndon Johnson, is the quarterback, and if he loses, how does he do in the next election? So don't lose. . . . He's living with his own political survival every time he looks at these questions."

Bundy criticized Johnson's manipulation of the deliberations over the war. The president "wants to be seen having careful discussions, and he does indeed want to hear what everybody is saying," Bundy observed. But that was the past master of the Senate at work, he said, "because that becomes part of the way a majority leader controls events -- you've got to know what the opposition's thoughts are -- so he finds out."

Strategy meetings and conversations on the war were a facade, Bundy said. "The principal players do not engage in anything you can really call an exchange of views. . . . That was prevented by him, and the process he used was really for show and not for choice."

The discussions Johnson valued most, Bundy believed, occurred privately and reflected his instincts as a dealmaker and consensus-builder. In the summer of 1965, Johnson's most important target was his commander in Saigon, Gen. William Westmoreland. Looking back on that time, Bundy said that Johnson viewed the general as though he were a powerful constituency wielding vital legislative votes. "Senator Westmoreland is like the leader of a block of some 20 senators, and you haven't got a good majority without him," Bundy said.

Johnson's shifting political calculations were often opaque even to his closest advisers, Bundy despaired, compromising the way the president engaged with his senior military and civilian counselors. "The process of decision, explanation and defense is unsatisfactory, frustrating, destructive and impossible to fix," he concluded in one of the dozens of plaintive notes he wrote for an unpublished memoir, a book he struggled with before dying of a heart attack at age 77. "No one knows but LBJ himself what the issues are, what his questions are aimed at, why he is deciding as he is -- or whether or when -- so if we really get to help him it is almost by accident."

As McNamara looked back at the pivotal decisions to escalate U.S. involvement in Vietnam, he recalled Johnson's resistance to confronting his advisers. "I am absolutely positive that most leaders wish to avoid confrontation among their senior people, particularly in front of them," McNamara said. "And that's a serious weakness. I think every leader should force his senior people to confront major issues in front of him."

'In Strategic Military Terms, We Quit First'

Then as now, the choice of a military strategy was the most crucial decision confronting the president...