Check the stats. 58,000 dead Americans vs well over 1,000,000 Vietnamese (North & South). Plus total economy obliterated for a generation or two.
Of course the outcome wasn't what American "commie fighter" policymakers wanted but the survivors in Vietnam would hardly consider it was the Americans who were smacked down.
The US would have "won" (I put it in quotation marks because it was never achieving much but human suffering) if it had stayed in just a bit longer. The last major NVA offensive basically used up their remaining reserves. Mistakes were also made far earlier that if avoided would have let the US win in the early years.
Sorry for OT, but a fairly good objective British documentary on the matter is Battlefield Vietnam: