On the "would Reagan have nuked Russia" question, a foreign-policy guru friend emails the following:

The likelihood of a President facing a truly existential, all-or-nothing decision to launch an annihilative strike against the Soviet Union ... was generally understood to be extremely slim, especially once the Soviets began fielding survivable nuclear forces capable of reliably reaching the U.S. Homeland. Far more likely - and indeed central to the course and, probably, outcome of the Cold War - was that a President would face the question of whether to employ deliberately limited nuclear strikes or conventional force (that might potentially implicate nuclear forces on either side) in response to some form of Warsaw Pact aggression. The core strategy of the Atlantic Alliance once the Soviets achieved intercontinental strike capabilities was Flexible Response - the capabilities and willingness to use varying levels of force, both conventional and nuclear, to deter Pact aggression and coercion and, if necessary, to impose costs upon the Bloc that would render whatever political objectives they were trying to achieve not worth the cost.  Because of the generally overwhelming conventional and non-nuclear superiority of Warsaw Pact forces for the duration of the Cold War (even in 1988, after the introduction of Revolution in Military Affairs-inspired weaponry and technologies, SACEUR General Bernard Rogers admitted that NATO forces would not be able to withstand a Pact offensive for more than a few weeks), it was NATO that necessarily relied upon the threat of resorting to nuclear weapons for its security.  Thus it was the Soviets who took a (kind of - their definition of "first" was quite elastic) "no first use" pledge, while NATO never did, always keeping the nuclear option open - and credibly so. 

Indeed, one of the key events in the Cold War was precisely a kind of speaking by deeds that the United States would resort to use of nuclear weapons through the crucial emplacement of the Pershing missiles in Europe in response to the Soviet deployment of the SS-20s. This was considered essential because the Soviets were perceived to be able to negate the credibility of U.S. strategic retaliatory forces by their own forces (thus essentially negating U.S. and allied strategic forces directed at the USSR itself), while also having potential theater (meaning European) supremacy due to their conventional advantages and their intermediate-range SS-20s.  The U.S. and allied decision to go forward with the Pershing deployments was the strongest signal possible that the U.S. and NATO would wage a war including nuclear weapons within the theater, meaning that NATO would go to the nuclear level on the ladder of escalation if necessary in response to Pact aggression.              

So the real question was: Would the President go across ... the "firebreak" from conventional to nuclear forces?  (This is a very, very different question than: Would the President let them all go in response to a total Soviet first strike?)  I think the answer has to be yes - that essentially every President in the Cold War would have done so.  The whole infrastructure of the United States - military, political/diplomatic (via NATO commitments, both formal and informal), intelligence, et cetera - were prepared to go nuclear, if need be.  The President was expected to, by his people, by his bureaucracies, by his allies - and, most importantly, perhaps, by the Soviets, who had to have a sense of the resolve of the United States from their sources, both public and private.  Even Jimmy Carter, our most liberal Cold War President, was the one to order the initial push to put the Pershings in.  He also signed off on Presidential Directive 59, drafted by William Odom, which pushed rationalized targeting policies for nuclear forces - a sign of seriousness.  

A more economical explanation for these kinds of retroactive pronouncements about never using nuclear weapons (McNamara has made similar claims regarding his advice to President Johnson) is that they take what was always a somewhat ambiguous posture (there were never strict triplines for nuclear use, for instance) and combine it with a desire to rehabilitate (McNamara) or apotheosize (Reagan) the image.  A more realistic and morally serious approach is to understand that we were deadly in earnest about our willingness to use nuclear weapons, the Soviets believed us, and so they never were able to cow Western Europe and Northeast Asia into submission.   

Finally, these retroactive statements that nuclear use was never seriously contemplated have very deleterious repercussions for future deterrence ... If countries don't believe the U.S. will ever use nuclear weapons, then these weapons lose any real effectiveness as deterrents. This would be a tragic development, and it would be the most likely route to their eventual use. 

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