As much as I'd love to be wrong, knowing what I know of Russians and their mentality, I can't see Putin being ousted anytime soon. He is just beloved in parts of Russia, especially among the older generation.
The contradiction is that most people don't want a war with the Ukraine but they will still support Putin because he is the strong man that Russian needs.
Who else is going to ride around on a horse bare chested?
I don't think it so much of Putin loosing the plot, after all this has been in the works since 2014 and isn't totally out of keeping with what Russians have done previously when 'threatened' by NATO expansion. I think this is more a case of the big gamble not paying off. Russia really did not expect this push back from the rest of the world/E.U., especially as it supplies much of the gas to the E.U. and we hardly did anything of substance when they annexed Crimea or when they supported the separatists in the Donbas or when Russian equipment downed flight MH17 over Ukraine.
Though now that the **** has truly hit the fan I still think they will tuff it out with Putin in charge. What clever and ruthless leaders do is to make sure there is no natural successor in key positions, that everybody can rally around to make an overthrow easier. (A bit like what Boris has done now.

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