Can’t see Russia invading all of Ukraine, just those parts where they think the population will want to be ruled by Moscow and not Kiev. Maybe firm up their situation in Crimea and add some parts of far eastern Ukraine. Not saying that justifies any invasion but that’s about all I would expect them to be planning to do, possibly take all the land east of the Dneiper then try to negotiate from a position of strength. Biden won’t do much about that, NATO might be more active if the Russians crossed the Dneiper. That’s if this isn’t just kabuki theater with some other objective.
They don’t even need to invade. Have those areas conduct a plebiscite and ask Russia to save them. Everyone will look at the situation the same as they did for Crimea.
Just like Hitler did in the Anschluss. Works like a charm against weak, liberal governments than and now.