From a Gallup poll conducted Dec. 31, 1965 – January 5, 1966 (N=1,545):
bq. What kind of rating would you give him (Robert McNamara) for the job he had done in running the Defense Department – A, B, C, D, or flunk?
bq. 18% A
14 B
11 C
3 D
6 Flunk
6 Don’t know
42 Don’t know who McNamara is
From a Harris Survey conducted Nov. 20-27, 1967 (N=1,600):
bq. How would you rate the job Secretary of Defense (Robert) McNamara has done on the Vietnam War — excellent, pretty good, only fair or poor?
bq. 42% Excellent/Pretty good
45 Only fair/Poor
13 Don’t know
There’s not much else in the Roper Center’s iPoll database, and nothing that allows one to track opinion over time.
UPDATE: Here’s Harris poll from Sept. 8-11, 20082006, that asked a similar question about Rumsfeld, albeit without a prompt about the Iraq War:
bq. How would you rate the job…Secretary of Defense Donald Rumsfeld is doing–excellent, pretty good, only fair, or poor?
bq. 10% Excellent
28 Pretty good
25 Only fair
32 Poor
4 No sure