Group 4 answer
Vietnam being called a mistake cause cynicism and public suspicion because the propoganda leading up to the war was so convincing, that for main media to go back on that, the U.S. Public was caught holding two contradicting beliefs.
These two beliefs were a) it was just for the U.S. to send troops into Vietnam and now b) it was a mistake to send u.s. Troops into Vietnam. This was hard for the public to accept because if they were to go back on what they were told before, what’s stopping them from going back on what they were saying now?