US and allies funneling weapons and intel to the Ukrainians, creating a bloody quagmire.

Success in that terrain requires air control, and Russia is extremely behind other major powers in stealth technology. I'm expecting that the West is flooding the Ukraine with air defense systems and experts to crash train troops on their use. Deny Russia the ability to provide close air support, and the defenders stand a much better chance.

Russia's economy is not great, nor is their military in a position for a protracted war of attrition.