Deterrent means exactly that . I don't think "first strike" features in any nuclear battle plan these days , even that of Trump and Kim , despite all the talk .
The Russians refer to it as a policy of “escalate to de-escalate”.
https://globalsecurityreview.com/nuc...ence-strategy/
Russia’s military doctrine dictates the use of nuclear weapons in response to any non-nuclear assault on Russian territory.