I think it is definitely a bigger issue than Ukraine. He does want to challenge Europe as a whole, but I think if he can take Ukraine, the next targets would be other post-Soviet states that are not members of NATO. He has those to bring back into the fold before he turns to NATO.
Of course, if NATO basically allows this.... That's why it's in the interest of Europe and why we're seeing this huge reaction from Europe. This has to stop now, because the long-term implications are really significant.