Just build nukes if you are afraid of Russia then nuke them if they try to invade. Ukraine is not as smart and gave up its nukes in the early 90s, and is now in the middle of a war for the last couple years.
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I'm broadly sympathetic to the argument that the multipolar world we're in now makes a good case for nuclear weapons adoption. But Germany probably isn't the one Europe wants to arm itself. And even if it did, their Greens wouldn't allow it.