There has been speculation that one of Russia's approaches to winning a conventional war which has become problematic is to use a small nuclear weapon to force the "enemy", whoever that might be, to negotiate terms for ending a conflict acceptable to the Kremlin. This doctrine is known as "escalate to de-escalate" *.
Quoting from the reference below, a U.S. Defense Department’s 2018 Nuclear Posture Review states:
“Moscow threatens and exercises [i.e., rehearses] limited nuclear first use, suggesting a mistaken expectation that coercive nuclear threats or limited first use could paralyze the United States and NATO and thereby end a conflict on terms favorable to Russia.”
and :
“Employment of nuclear weapons can radically alter or accelerate the course of a campaign. A nuclear weapon could be brought into the campaign as a result of perceived failure in a conventional campaign, potential loss of control or regime, or to escalate the conflict to sue for peace on more favorable terms.”
end quotes
According to public comments from Russia, the escalate to de-escalate doctrine is not part of their strategy on the use of nuclear weapons.
Quoting from the same source:
"The Kremlin reaffirmed in a 2020 defense document that it will only consider the nuclear option under two circumstances: 1) as a retaliatory measure against the use of nuclear weapons or other WMDs, or 2) when “the very existence of the state is in jeopardy.” "
end quote
Based on the Kremlin's repeated denials that it would invade Ukraine, one cannot have a great deal of confidence in their public claims regarding warfare of any kind. Since things are going rather badly for the Russians, with an apparently developing stalemate and continuing heavy losses, some think Putin may be considering his alternatives. Knowing Putin as the world does at this point, with his murderous attack on Ukraine and its civilians, the employment of a nuclear escalate to de-escalate policy clearly cannot be ruled out.
One can only wonder how Ukraine, and NATO, would respond.
"Russia’s Crazy Nuclear War Strategy: Escalation...to De-escalate? "
* https://nationalinterest.org/blog/bu...scalate-180680