Does Putin have the domestic political power for such a massive war, though? Putin's Russia isn't the USSR, where the deaths of Soviet soldiers in Afghanistan could be covered up. The word will spread that Russian troops are getting killed in Ukraine by the "brotherly" Ukrainian people. Kremlin propaganda can only dismiss these as acts of fascist provocateurs for so long.
When Crimea was taken in 2014, it boosted Putin's domestic popularity because it cost zero Russian lives. Then he tried to repeat the trick in the Donbass, only to encounter Ukrainian resistance. He maintains the fiction that Russians aren't involved in the Donbass to this day, because he can't admit at home that he made Russians die for...half of two oblasts.
As for sanctions, well, Putin and his buddies have stashed their wealth in the countries they publicly despise. If the US was really, really into psy-ops, it could declassify documents about the apartment bombings, though the timing of that will be key.
I think the domestic condition of Russia is Putin's actual motive. These so called demands for "security guaranties" is nothing but rhetoric. Does he or anyone else seriously believe that NATO would invade or attack Russia? Come on, it's not going to happen as preemptive military action. What Putin needs is an enemy outside of Russia that he can blame for his gross economic missmanagement and the immense wealth inequality in Russia. Furthermore, he doesn't want Ukraine to become a prosperous country with peace and freedom, because he fears the Russian people demanding the same then. That's why he actually has no desire for normalized and stable relationships with the US or even the EU. He's a thug and bully, still in this Cold War mindset that each "superpower" should have its sphere of influence.
