The Bulletin of Atomic Scientists has a fascinating post up, “Why Russia calls a limited nuclear strike “de-escalation””.
See, the US (and NATO more broadly) developed the category of “tactical” nuclear weapons in the 1980s to counter perceived USSR conventional superiority. (Notably the Pershing II missile, from 1981-89.) The Soviets were having none of that — their stated policy was that any use of nuclear weapons would be considered a full-on strategic strike, and would be retaliated against accordingly.
In our time, though, the Russians are saying they might resort to tactical nuclear strikes, because of US conventional superiority, as demonstrated in Kosovo, Iraq, Afghanistan, etc.
(h/t, Elisabeth Eaves, on Twitter.)