Russia is deploying S-400 missile defence systems in Sevastopol, Crimea, for "protection from Ukraine". According to Putin's Press Secretary Dmitry Peskov, this should not be perceived as a threat to anyone.
However, it is clear that there is a threat for Ukraine coming from Crimea, as, according to Shoygu, a self-standing military group has been created there, and the very fact that Russian military-political leadership views or presents this situation as potential defence capability, is already a sign of a dangerous arms race and militarisation on the peninsula. The threat is perceived not so much as an actual threat, but as perception of this threat by the country that is preparing to fight off similar aggression. And one of the steps is a preventive strike, so, if at any moment, Russia feels that it is not enough to have equipped themselves to fight off any aggression, in theory, they could legitimise a pre-emptive attack as defence.