He's been allowed to get away with so much before that this has always been on the cards, although I have to say I think Biden has dealt with this difficult situation reasonably well - sounding firm without sounding bellicose, just exposing Putin's lies.

Problem is what to do about it - if he doesn't meet any resistance he'll take more territory than his rebels have already taken from Ukraine, and if Ukraine tries to retake/protect its own territory Putin will say it's a form of aggression, and will use that as an excuse to keep going and take even more territory. They're damned if they do and damned if they don't.