The MAD argument still applies: Ukraine can't threaten to nuke Moscow without Russia obviously threatening to retaliate with nukes.
Ukraine isn’t in and probably never will be in a position to credibly threaten a MAD second strike to Russia. From number of warheads to strategic depth, it’s not a realistic option. Instead it would seek to credibly threaten limited nuclear war using tactical nukes.
This would only make sense with European support. And at that point, it almost makes more sense for Europe to directly enter the fight. (Or give Kyiv the nuclear weapons.)
Both sides have to agree to the "limited" part for it to stay limited. Mind you, threats of nuclear escalation are routine from Russia.
It’s more that each side has to moderate itself. That’s true if both have nukes or just one. And it’s much easier to moderate oneself when it’s in one’s own interest, e.g. to avoid getting nuked.
If you mean a scenario where Russia uses its entire arsenal at once, I think I would agree — but that would leave them extremely vulnerable to everyone else. Even without that, between the shared border and the nuclear reactors, lots of fallout would end up in Russian soil, in their farms and food.
For the size of nuclear strike that would allow Russia to not hurt itself directly by the attack:
If Ukraine found a some still-functioning nukes lying around in a formerly-locked Soviet-era cupboard, what would stop them from being so already with current weapons?
Russia doesn't seem to be able to prevent conventional strikes by Ukrainian forces. Is that only due to US assistance with materiel and intel?
They can always just stop? It's not as if Ukranian tanks are at the gates of Moscow, it's more like the US withdrawal from Afghanistan. Or the previous USSR withdrawal from Afghanistan.
It is unclear whether the UK or France would threaten a retaliatory strike in case of nuclear weapons use not against their own territory. It doesn't seem likely, but if there's one thing Putin is very cautious about it's his own personal survival.
They can, but that is what I am wondering about. Will a desperate Putin think he can get away with a nuclear first strike on Ukraine? If he thinks he can, why stop?
Considering that the Russian government continues to sell this invasion to its people as a "special military operation" and bans calling it a "war", what impact would using nuclear weapons have on the internal politics of Russia?
I also invite you to consider the converse: Ukraine is already asking if it made a mistake by giving up its nuclear weapons, and I have heard plausible claims they could construct a nuclear device within a few months… a few months ago.
The US withdrawing all support, may well result in Ukraine making their own nuclear weapons — and attacking Russia with them to make the point, given that Putin seems to have great difficulty understanding that the Ukrainian people don't want him.
May be you mean uranium enrichment? When plutonium is already available, like in Ukraine, it is completely different game - you just need to chemically separate plutonium from the spent fuel. That is the only noticeable expense - needs facility with safety protections, etc. Or just a few people willing to die for the Motherland. The rest is putting charges around the plutonium sphere and timing them correctly with electronics. That is basically all. Couple weeks really :)
Which is fortunate, because it's also quite easy to make plutonium by exposing (natural or depleted) uranium to neutrons…
They need to develop bunker busters though.
Btw, according to the Russian nuclear doctrine nukes can be used when the country is invaded even with just conventional weapons if the invasion presents severe threat to the country. Thus according to the Russian nuclear doctrine Ukraine is allowed to use nukes.
Let's not forget these folks have their self preservation in first order, the population is just a means for their survival.
That's why it's imperative for Ukraine to have bunker busters, like gravity bombs, because the first strike would need to be where the leadership is.
That is also notable in the context of Trump yelling at Zelensky that Zelensky is supposedly playing with WW3. If anything, by not making nukes Zelensky shows an, unreasonable at my opinion, restraint here.