@PestorPeston
I was also thinking that there was potential that if Russia can't have Kviv nor can Ukraine. With justification along the lines of, they are all Nazis, only way to oust Zelenskyy (who is the most evil man on the planet), cleansing our brother country's rotten core.
Why not just do it right now then, if thats your thinking?
Why withdraw your troops, say you are doing so because you need the leadership of Ukrainian to settle the war, and then nuke them? Why go to the apparent effort of clearing up bodies in Mariupol to hide astroscities with a mobile cremation unit, only to nuke Kyiv? Why make a song and dance about war crimes not being done by Russians only to nuke Kyiv? This is being done for two audiences: the domestic one and the wider non western one. Dropping a nuke isn't hideable.
I guess if you wanted to make a point of doing it you'd probably pick May 9th. But otherwise, it has no strategic benefits.
Chemical or biological weapons is another matter. Russia are making ominous noises about this. But the suggestion is the target would be in areas they want to cleanse of pesky Ukrainians not the capital. So they can blame Ukrainians.
The signs are now that Russia must be digging in for a long entrenched war - if they have accepted that reality, then actually the risk of 'an event' reduces.
Where this becomes a risks again is if the Ukrainians manage to hold off a regrouping and then push back against the Russians.
Because that starts to look like Russia can claim no victory at all.
Even if you go down the mental gymnastics of Kremlin moving goalposts there are certain consistencies: 1) Putin wants to stay alive 2) Putin wants to stay in power 3) Putin is reluctant himself to use nukes because of 1 and 2 4)Putin will use chemical weapons but also has to find a way to justify / blame their use on Ukraine because there is still a need for the veneer of plausible deniability / destruction of the truth.