Why do you think Russia is cornered?
Russia continue to gain ground in the Donbas. Gain/Lose around Kharkov and Kherson. Except for their first attempt to get the entire Ukraine gov't to crumble in the first couple weeks, Russia just keeps on winning.
Yes, it is a grinding war, but that is to be expected after Ukraine spent 8 years building up defenses in the Donbas explicitly expecting this war (Poroshenko said they never planned to implement Minsk, they just used it to "buy time to prepare for the war" - his words).
Russia's economy took a hit, no doubt. But it is not crumbling. Half the planet is either supporting Russia or abstaining from speaking out against him. Pentagon officials don't see Russia capitulating.
So again, what corner is he in?