Colin P said:
Another similarity is that the US did not want to get dragged into either conflict. When approached by guerrillas that fought the Japanese alongside the Allies to support Indochina Independence, the US balked and choose to let France move back in, when France made a mess of it, the US were sucked in to help them. In Afghanistan, once the Soviet threat was gone, the US walked and could not care. The Clinton's were ready to make a pipeline deal with the Taliban, until Women Lib lobby groups forced them to stop. Both started out as "Not our fight", but when the worlds superpower, it's always your fight.....
Yep, and there's got to be a lesson in there somewhere. Something about "must-do's" that look more like "shouldn't have done's" in hindsight indicating requirement for a more critical analysis of the core U.S. national interest up front, or perhaps accepting that they are "must-do's" and making a more honest analysis of the conduct of the wars to see how we could do better.
However, the institutional culture seems be retreat to the "conventional" world the moment the "dirty" war is over. I view the effort in some circles to characterize the conclusion of the Vietnam war as a conventional fight that the U.S. could have won but walked away from as a part of that proud tradition. As LGen McMaster has written on Vietnam, Afghanistan and Iraq, we as military professionals do ourselves a great disservice when we ignore the political dimensions of conflict.
Colin P said:
As for letting the Soviets bomb South Vietnamese docks, highly unlikely they could or would go that far. The US would have to give the Soviets warning to ensure their ships had time to get out, but once the docks and cargo handling equipment is destroyed, Soviet resupply would slow. Likely they would need to be bombed every 6 months to ensure no proper repairs are completed. Also bombing other areas off limits would have helped. No doubt those "Russian speaking, Slavic looking" Vietnamese pilots would be trying to shoot down the bombers.
My point there is that it was not politically feasible for one reason or another at the time, and that you are going to find those kinds of limitations in a limited war. That said, there were Soviet and Chinese flagged ships in port when the U.S. Navy mined Haiphong harbour in 1969, so I'm not sure that the U.S. had any real compunctions about disrupting that traffic another way.
The broader issue is what Journeyman has alluded to above. The narrative of "if only we could have bombed this target or had that ROE" doesn't hold water in either conflict, especially in Vietnam. Ultimately, the NVA with very limited (compared to what the U.S. had put into the south) Soviet and Chinese assistance won the day without disrupting the ARVN's strategic supply lines. There is a reason for that, and that reason is fundamentally political.
The NVA and North Vietnamese government enjoyed significant, though by no means universal support in the south, which provided them with local resources and personnel. I have read accounts that 40-50% of the NVA fighting troops and upwards of 80% of their support personnel (porters, scouts, etc.) were from the south. Meanwhile, support for the South Vietnamese government fell apart as the NVA gained momentum, which contributed to the disintegration of the lavishly equipped and thoroughly trained ARVN*. That political issue led to the strategic failure, and that is what the U.S military and associated diplomats should have been focused on. Instead, the military adopted a largely conventional approach (reducing the local popular support in the process), while the diplomats backed a losing horse.
*There is a striking parallel there with the Iraqi Security Forces breaking in the presence of a small number of ISIS fighters in in Mosul in 2014. If that doesn't serve as a cautionary example, I don't know what will.