As if YOU would know "actual" history
The USA had been involved in Vietnam since the 50'ies - massively providing arms, intel and support to the French.
Kennedy knew that Green Berets and other instructors couldn't turn the tide in South-Vietnam - so he decided (with full support by Congress) to send the first regular US troops to SV. LBJ then made a full fledged war out it (with full support by Congress) - targeting North Vietnam and ordering illegal bombings on Laos and Cambodia.
Nixon first (with full support by Congress) even expanded that war to Laos and Cambodia by ordering a ground invasion into those countries. After filling the last 58,000 body bags - someone told him that the war isn't winnable - and that the Democrats might win the next election if he won't put and end to the Vietnam war - The Paris Peace Accords were mainly pushed by the United States, led by President Richard Nixon and National Security Advisor Henry Kissinger, and not by North-Vietnam.
And every reputable US staff officer having served in Vietnam was fully aware that the South wouldn't stand a chance - so factually the US BETRAYED its former long time ally.
Now that FACTS and HISTORY - not your war-comic knowledge