Earlier quoted context omitted.
It's impressive how deep some of these psychological things run nearly 50 years on. It was such a blow to self-image that, let alone all the related domestic political fallout, people still have a hard time accepting what happened. The sheer amount of ink and celluloid spent trying to come to terms with this is awesome, and a little depressing.
How many wars did the US win (as in "achieved the political goals") since WWII? Korean war: half won, half lost. Vietnam war: lost. Grenada invasion: sort of won. Gulf war 1991: I'd say won, despite Saddam staying in power. Gulf war II: I'd say lost, despite Saddam deposition. Afghanistan: lost, despite the killing of bin Laden. Syria: can't tell yet. It's a pretty depressing tally. With that, I'd say that the US was…
That said, many of the well-known, long haul conflicts that the US are involved in are the ones they are most likely to lose. The ones they win they usually win quickly and are less well known.
There are plenty of interventions post-WWII that have been quick successes for the US, esp. in Latin America.