How about getting a competant, efficient, honest (or at least democratic) regime in Saigon? Then Vietnam would be a lot less UNpopular....Your challenge, should you accept it, with a POD no earlier than 1991 and no later than 1993, is to have a US invasion of Bosnia as unpopular as the Vietnam war.
Brownie points for Jade Fonda (or her equivalent) going to Belgrade
Have a lot of Yankee soldiers killed, and have them conduct some Song My like massacres. Quickly people would wonder why their sons and brothers are sent somewhere to die or become immoralized.