What a stupid push question this is. Defend it now or retake it later is the question. Russia will not stop until either it collapses or it is defeated. Ever read ANY history? Rhineland or Sudetenland ring any bells? How about “Peace in our time”? When we had them down we should have put the boot in instead of leaving them bases and strength to begin again. Germany and Japan are allies because we demonstrated strength. With Russia, Bush wimped out and here we are again. Get a clue.
Not nearly as badly as Roosevelt did decades earlier.