Much simpler, lower cost strategy would have been to invade Cambodia and capture the entirety of the Ho Chi Minh Trail. One northern general stated that if the US had done that, the war would have been over in 6 months. It’s all about supply lines.
Destroying the dikes and dams surrounding Hanoi during their rainy season would have caused at least 100,000 to drown.
Supply lines are no good if there's nothing to supply. If we had bombed Haiphong and Hanoi into rubble, smashed the NViet irrigation systems and dropped Agent Orange onto their rice paddies, North Vietnam would have struggled to feed their own people and would have no capabilities left over to bother the South.
We were unwilling to fight as we fought WW2. And so we lost.
Or, simpler still...
Invade North Vietnam.
And promise to use tactical nukes - ONLY in North Vietnam - if Russia or China responded with ground forces.
I'm not a war historian, but I can't recall a single war between bordering countries where one country - North Vietnam in this case - had NO FEAR of a counter invasion.
I recall reading a science fiction short story back in the day that suggested salting the Ho Chi Minh trail with highly radioactive material (plutonium?) embedded in multi-ton contrete blocks.
IIRC, they would be helolifted into place with the crews being protected by lead shielding in the aircraft and by remotely controlled, drop-away lead shutters on the blocks. After being deposited, the shutters would be activated, fall away, and the entire area would soon be flooded with lethal doses of radiation. Placed densely at critical choke points, the blocks would present a human-fatal barrier that would stop travel on the trail.
Of course, the fatal flaws in the theory are: 1) that even fatal overexposure to radiation is not INSTANTLY fatal and 2) that, when called up to accomplish a higher purpose, human beings will deliberately volunteer to work in such environments - to expose themselves even though death is considered certain.
The firefighters at Chernobyl proved that. (The jury is still out on Fukushima.)
(Glad it wasn’t tried - got enough problems in Vietnam and elsewhere from Agent Orange)