Trouble is, Putin is operating without any restrictions which will allow him to do whatever he wants in Ukraine, and if that's allowed, there's nothing that will disincentivize him from going beyond Ukraine. There has to therefore be a strong line of demarcation that will result in NATO taking action before he completely decimates Ukraine and its population with chemical weapons, thermobarics, false flags involving some sort of WMD, or just general incompetence that results in a nuclear reactor spewing radiation across Europe. Biden and NATO are playing this a bit too safe at the moment, which is actually incentivizing Putin to be more brutal within Ukraine, because he suspects those watching him don't have the courage to stop him.