Certainly I have read history on this
I also lived through it.
It is not true that the American public was never promised an end to the war (forgive the double-negative). Numerous administrations promised (including LBJs), none delivered. The American public lost patience. The hated protesters were part of the patience-losing process.
Really, Larry: aren't you glad that we aren't still fighting there?
Yes, there were things that were done poorly in Viet Nam. There were also things that the American services did brilliantly well. This is true of every war we have ever fought.