If you believe that the tragedy of the Vietnam war was due to one man, I have a bridge to sell you. The sheer hyperbole of saying that greatest disaster in American history was a single man should make you immediately question the speaker. Note that this quote was from a 2009 interview - so Baker had Nixon, 9/11, Iraq/Afghanistan and all the other much, much darker times in American history to choose from.

I would also reject that the idea that he was a particularly bad actor in the Vietnam War. There were so many presidents and generals that didn't realize what was happening and messed things up royally. Just read about how out of touch Westmoreland was. This is like blaming the goalie or the kicker for losing a game when it's actually the combined efforts of the whole team over the entire game that wins or loses a match.

The other speaker in the quote is Ford - who we should note is called by Iacocca as 95% jerk - apparently, he didn't get along with anybody.

Other people credit McNamara and his fellow Air Force buddies as turning Ford around after World War II. Wikipedia even says that Henry Ford II made him president (although it was only for 5 weeks).

(I'm not a defender of McNamara, but I also think this lopsided view of him is unjustified - we need to have nuance in the way we view people)