You raise a very strong issue: is there the encirclement of Russia? If I were Putin and i’d ponder along these lines my first reaction would be not to wonder about the legality of this but how to get out of the encirclement. In this case Putin did the first right thing: approached China. But China is not going to go all the way against US and Europe to save Russia. To China Russia is important as a land bridge to Europe, but if Moscow blocks its dealings with Europe (or cuts them down significantly) then Russia turns from a land bridge into a huge drag economic and political drag that can damage China immensely.
So Putin should be clear that China can help but it is a long way from being a total solution. Therefor, if I were Putin my priority would be not how to destabilize Ukraine, but how to avoid the encirclement i.e. being destabilized. In fact, it turns out that by destabilizing Ukraine Russia is getting destabilized and encircled. Ukraine can turn into Afghanistan n.2 for Russia. Does Putin want it?
Then if I were Putin, encircled, pressed by low oil prices, I would withdraw from Ukraine as soon as possible, regroup, rethink and live to fight another day.
As for the US, if I were American, worried about aggressive Putin, i would think that the goal there stop Putin, reduce him size but not break down Russia, something which can be very “distracting” when the real deal is cope with the China rise and the growth of Asia. But perhaps some in America could be thinking that if Putin does not step back then breaking down Russia might turn out to be a necessity.
There are a lot of suppositions in this lime of thinking, but should not be like that when forecasting chess strategy?