If the US had concentrated on economic targets (destroying the dikes in North Vietnam and ruining the rice harvest; taking out the warehouses in Haiphong; etc) and gotten the North too busy keeping its own people from starving to look for trouble down South, things might have been different
Now I certainly am no expert when it comes to war, but I would have knocked the he** out of the North. It was politics, right, all politics? Seems to me we were totally destroying the wrong part of Vietnam.
The biggest problem was president johnson micromanaging the war. He personally picked bombing targets. When the president has that much distain and mistrust of the military, there is no way the military could function. And when we did withdraw, we failed to support the South. So they were unprepared to fight alone.