By the US and allies.
Not a direct military attack — Russia still would have a superior military — but new Cold War.
Very similar to what has happened right after WWII.
Specifically, massive sanctions and pressure on the entire perimeter, perhaps even including the Chinese border — if China is defeated.
And this is the scenario Putin must avoid.
Totally ridiculous. For what reason would the allies want to attack Russia? How is it in any of the allies interests to attack a nuclear armed Russia after fighting a war against China.
I really don’t think you’ve thought this through. Try it using this template; the Allies and the US would much rather have good relations with Russia and do business with them than attack them for no reason and risk nuclear thus the deaths of perhaps a billion people and the worlds infrastructure completely destroyed.
You honestly believe the Allies would attack Russia for no reason?