This proves beyond reasonable doubt that Donald Trump is not at all qualified to sit in the Oval Office.
The US and NATO alliance is the only thing that prevents Putin from invading the whole of eastern Europe and recreate a sort of USSR. And after Brexit he is vastly more confident that the EU might eventually crumble, removing any economic incentive not to invade off the table.
The US-NATO alliance has survived the cold war. I'm afraid it wouldn't survive a Trump administration.