We more or less did. In fact we slapped the gooks so hard they signed a peace treaty and we pulled most of our men and equipment out.
The only actual chance at outright military defeat we faced was the Tet Offensive, which failed spectacularly.
Then the Vietcong, being lying commie scumfucks, broke the treaty and sneak-attacked the south again, stretching the war out another 3 years with half our equipment back in the US until we just said fuck it, cut our losses and left the South Vietnamese to die under commie bootheels. Domestic support for the war fell off a cliff for various reasons, the soldiers were sick of fighting a war they thought was already over, and the logistics just weren't logisticing anymore.
Contrary to what people (perticularly anti-US people) like to pretend, the Vietcong never defeated the US. There was no great final battle where the noble Cong blew up the Yanks until they surrendered or anything. America just kinda... gave up and went home after a while.
It's the perfect example of soldiers doing everything right but still "losing" because retards with stars on their shoulders didn't think ahead.
It's like if a boxer was beating the fuck out of his opponent, then his opponent smoked a bunch of meth between rounds to stay conscious and the winning guy just got tired halfway through the 10th round and threw in the towel so he could go home and take a nap.
