In 1965 we had 9,345 strategic warheads while the Soviets only had 929.
We had a 10 to 1 advantage.
It would be foolish for the Soviets to respond because we were the ones who had nuclear superiority.
929 warheads is still a lot of warheads. How many do you need to wipe out civilisation?
So we pop off a nuke in NVN and suddenly one goes off in Taiwan. Now what? Even with a 10-1 nuclear superiority, do you really want to get into a game of global tit-for-tat?