Putin doesn’t need to do anything. The Yurps have shown themselves to be not real allies for well over a generation.
Its long past time Uncle Sugar stopped subsidizing them so they could blow more money on socialism. Withdraw from Nato, bring the boys home and strike mutual defense pacts with the few real allies we have like the UK, Poland, etc.
US would not leave Europe vulnerable to a United Russia/China military, which they are currently forming. That’s just not going to happen.