99% of the west including all western politicians seriously believe this. Putin is a deranged and unstable dictator except when it comes to nukes where he suddenly becomes a pacifist.
I don't see how this conflict doesn't end with a nuclear conflict between America and Russia. America is finished either way with Trumpists and the Democrats at each others throats. Maybe the establishment wants to go out in a nuclear fire rather than a long and bloody civil war?
China will step in before Russia goes nuclear.
The logic and calculations are simple. If Russia starts lobbing nukes around, the chances of MAD between Russia and America rises beyond acceptable levels. If there is nuclear MAD between Russia and America, America and the rest of NATO will also launch on China since they got nothing to lose at that point and will not tolerate China coming out unscathed (relatively) and becoming the dominance power and race.
I see China kicking off AR before Russia presses the big red button, which should instantly relieve pressure on Russia as American attention snaps to Asia and Ukraine’s weapon gravytrain suddenly derails.
I don’t really see direct Chinese military intervention in Ukraine because it will suffer basically the same economic sanctions from the west in that event as AR, so why not maximise Chinese interests first and foremost?
Also, in the event of AR, China can always hold direct military intervention in Ukraine over the heads of the Euros to try to stop them going all in with America on sanctions. Unlikely to work, but might as well try since there isn’t much cost or much more for China to lose.
I just don’t see Russia actually going nuclear over Ukraine because A) They are nowhere near being actually defeated. They have yielded ground, but have not suffered any major military defeat or lost significant forces or capabilities. B) China will step in to relieve the pressure one way or another before Russia feels it has to go that far.