I wouldn't be too concerned about Russia. Putin can't even take a small land with 6 times less citizens in the "two weeks" that he boasted he could do that; and Europe is an entirely different beast. But it is true: When America loses its allies, it loses everything. That is what Trump is doing.
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The Russians can’t win a war in their own backyard, even bolstered with mercenaries and North Koreans. I don’t think Warsaw and Berlin are in danger of occupation.
And Putin is 72, is terribly afraid of being assassinated and is indeed surrounded by enemies who just wait for an opening.
This problem will solve itself. Soon.