Lots of left wing people want to say we shouldn't forget the lessons of Viet Nam. I always reply back that we shouldn't forget the lessons of WW I.
Most people get the lessons of Vietname wrong anyway. The thing about the Vietnam war is that we had BEATEN the Viet Cong by the early 70s. It took the full-scale invasion of a conventional army to make South Vietnam fall in 1975. The US definitely had the firepower to stop that--we could have done it from the air. But, by that time, the Dems controlled Congress and we had lost the will. Of course, it didn't help that the South did a crummy job of defending itself. [Unfortunatley, I suspect the current Iraqi regime would have a similar meltdown if left tommorrow]