How would the US detect attempts to develop nuclear weapons before any tests took place? Should they have nuked the USSR on a well-founded suspicion?

I think from a rational perspective, the answer must be yes. Under this hypothetical policy, if the USSR didn't want to be nuked, then it would have done whatever was necessary to dispel the US's suspicion (which of course it would have voiced first).

Do you really prefer the alternative that actually happened? That is, allow the USSR and many other countries to develop nuclear weapons and then depend on MAD and luck to prevent world destruction? Even if you personally do prefer this, it's hard to see how that was a rational choice for the US.

BTW, please stop editing so much! You're making me waste all my good retorts. :)