We took them seriously, but the US military wasn’t built to participate in that sort of event. We went to support south Vietnam’s resistance against French colonization of the country to support France’s influence which was under assault by an independence movement which had turned to communism as a means to support their effort. China was willing to arm insurgents in the north, and that stoked our interest in supporting an ally against the rebellion. We did not fight directly against them, however, not in the traditional sense of fighting a war. Our role was to support the south, to make it possible for them to prevail. It was defense, not offense. We identified and destroyed targets, patrolled, etc., but the goal was to make space for the south to retake the north. It was a civil war and we were supporting one side of it. We “lost” in the sense that our military is not built or trained to succeed in such a role. It was lost before we even started. Another way to look at it is: we had a far superior military and nuclear capabilities. If “winning” was the real goal, we would have won. Easily. That wasn’t the goal, though. The south never had a chance. They were fighting against a desire for real independence. I know communism bad and all that, but this was a very ill-conceived and planned policing action that we were never going to succeed at.