Any outright invasion of Lithuania will invoke NATO Article 5. The Poles would respond regardless, and with a newly organized territorial militia, any Russians in Poland would get a very “warm” welcome wherever they were.
Poland would also respond if Russia threatened the rest of Ukraine beyond the Donbass and Crimea. They would move into Western Ukraine.
I pray Putin isn’t that stupid, and just doing some sabre-rattling for domestic consumption.
NATO will not be able to do anything.
How many EU divisions will march against Russia? We couldn’t get to Lithuania, let alone defend it.
They could invoke but take no real action, depending on the state of the rest of the world at the time he made his move. I still think we sent a subtle message to only put troops in Poland, that we wouldn’t necessarily fight as hard for Lithuania.