How can you compare Warsaw to Hanoi? One city is next door, and the other is thousands of miles away. I disagree that there was any hard evidence that the Soviets would engage in a nuclear war with the US over cities outside the USSR. Empty bluster, yes. Real evidence, no. Havana is a good example. Certainly is was a better strategic partner for the Soviets than Hanoi, yet when confronted they backed down. Had we actually invaded Cuba, in my opinion the Soviets would have done nothing.
Perhaps the Chinese would have invaded to try to stop the US from capturing North Viet Nam from the communists. Are you claiming that US forces could not have stopped them? I think the B52 fleet, combined with naval airpower, would have been able to make sure that the Chinese regreted any invasion.
Anyway, you and GunnyL have criticized my suggestion that North Viet Nam should have been invaded in order to secure victory in Viet Nam. GunnyL wrote above that victory in Viet Nam was possible, but unless I missed it above, he did not state how such victory could have been accomplished. Do you think that victory in Viet Nam was possible? If so, how?
I think that if we were going to tie the hands of the military and block an invasion of the North, prevent intradiction of supplies no matter where that needed to occur, and forbid attacks on the "civilians" that backed up the North Vietnamese war effort, then we should have never went to Viet Nam in the first place. We should have just declared defeat from Washington, and saved ourselves much blood and treasure. The fact that Johnson turned our combat forces in Viet Nam into some gigantic police force, confined to a corner of the battlefield where the supply lines to the North and the "civilian" supporters of the enemy were outside the zone permitted for combat, was an extreme miscalculation that turned our soldiers into targets of the enemy without giving them a chance to win. Bush as made precisely this same mistake in Iraq.