"Did the US military lose South Vietnam?"
No, I said they weren't allowed to fight the war to the best of their ability. You can blame the Democratic Congress at the time for the bloodshed that followed our withdrawl but it is the American people who ultimately made the decision to wash our hands of all things Vietnamese. That includes all the war protesters and the "silent majority". What I find most disturbing about South Vietnam is that after all we invested there, the spark of freedom didn't ignite anything and they layed down for their own slaughter. Unfortunately, I believe the same thing will happen in Iraq after we leave. A thug will fill the leadership vacuum and they'll be back to square one. I sincerely hope I'm wrong on that one.
I think you forget that the Vietnamese War was thirty years long. By 1975, all the Vietnamese were pretty sick of war, but the North Vietnamese army was intact. In the case of S. Vietnam, the line was not held. In Korea it was, and as a result authoritarian government has been allowed to develop into democracy. Perhaps if we had done something like the enclaves that Jim Gavin proposed, the line might have been held. If we had pulled out of Korea after the Armistice, do you think that the ROK forces could have held off the North?