Remember: Russia has been invaded many times from the West. Therefore, it needs client/vassal states on its border to give it some protection.
Poland, on the other hand, has been invaded many times by,.... Well, by Russia. So this just means that Poland needs to bow down before its overlord.
Ukraine - well, that's not even a real country (according to many a Russian social media troll).
More seriously, The E.U. seems more and more centered around Germany and Poland, instead of Germany and France like it used to be. Poland also seems to be pretty enthusiastic about its participation in NATO, and Russian antagonism towards Poland and Ukraine provides a nice continuation of the justification for NATO's continued existence. Poland will not be back under the Russian thumb anytime soon.
Then again, Putin is showing again that he's a master at destabilizing things in ways that are almost impossible to anticipate. He's an effective opportunist who can move quickly to take advantage of whatever cracks open up when he gives his western borders a good shakeup.
He's the Fidel Castro of the 21st Century, the domestically popular (enough) dictator that keeps poking the west and who will likely remain in power for another few decades.