[cmrdporcupine]

Sure, but as the commenter above you was saying, it wouldn't be an "invasion." It'll be a series of escalation provocations. Blow something up "by accident", poisonings of escaped dissidents, "little green men" stirring stuff up in the "persecuted" Russian-speaking minority, and then using that as a pretext for more and more strident interventions.

And at each point NATO has to make a decision whether it's "worth it" to escalate into armed conflict over it, and Putin can just keep "bending the stick" until he finds where it's about to snap, and not push any further, while the stick gets a bit weaker and weaker...

I do think the Russians are vulnerable right now in the sense that if they provoked excessively in the fashion they were used to before the invasion of Ukraine, they could open the floodgates to more serious support for Ukraine.