In this scenario of conventional aggression and defence, the control of the level of military risk to which Russia is exposed is entirely in Russia’s hands; Russia can withdraw if the costs outweigh the anticipated gains.
Many people equate deterrence with nuclear weapons. But even nuclear deterrence is about convincing an aggressor that the defender is resolved to take punitive action if the aggressor follows a course of action, and the costs the aggressor faces would outweigh any potential gains. But in this case, the control of the level of risk to which the aggressor would be exposed is now entirely in the hands of the deterrer, and with nuclear weapons, those risks are incalculably large.
The visceral fear that nuclear weapons engender inhibits the use of even conventional force between nuclear powers through a fear of escalation. This is at least one reason why the USA and NATO have been quite clear that they will not participate directly in the defence of Ukraine against the Russian invasion; and Putin knows it.
All sides in a conflict can deter. Indeed, they try to, all the time and will deter each other simultaneously. Rational nuclear powers would only ever use nuclear weapons for deterrence purposes; that doesn’t mean they would never detonate one, but any detonation would be for the psychological purpose of reimposing deterrence rather than any military purpose such as destroying a bridge; it is the crisis that needs the weapon, not the target.
Most nuclear deterrence consists of messaging; changes in force posture, training drills or deployment of weapons systems (not tweets). On 27 Feb, Putin started engaging in some explicit nuclear deterrence. By announcing that Russian deterrence forces would move to a ‘special regime of duty’ he raised the profile of nuclear weapons in his invasion of Ukraine. The actual changes appear, while not trivial, minor, and there are no indications that Russia has materially changed weapon system deployments or readiness. But by simply mentioning the N word, Putin seeks to focus the public discourse in Europe and the USA on nuclear deterrence in an effort to influence decisions about future interventions.
Putin’s statement also suggests coercion against Ukraine; since 2014, Russian military doctrine allows for the use of nuclear weapons to avoid conventional defeat. He could be trying to suggest to Ukraine that they must consider the prospect of a nuclear attack. I’m not suggesting any such attack is more likely; but the announcement almost certainly seeks some influence on Ukraine’s decision-making process over the next few days.
Russia did much the same in 2014 during the annexation of Crimea; arguably, it worked. This time however, the international community appears to be taking a much more coherent and resolute stance in response to Putin’s antics.