The U.S. doesn’t stand to lose anything by accepting Poland’s generous proposal and gradually relocating troops there from Germany. A move of this kind would be consistent with stated U.S. goals, such as deterring Russia. It would also allow the U.S. to support an ally eager for closer military ties.
It might also force Germany to give more thought to its position. Would it feel unprotected with a smaller U.S. presence? Would it, perhaps, be motivated to enhance its own defense? Or would it still be secure in its apparent conviction that no one is interested in attacking it?
The U.S. should offer protection to the countries that want it most, and reduce its involvement with nations that benefited in the mid-20th century. The American military presence should be aligned with its allies’ sense of being threatened. This anxiety gets stronger the closer a country is to Russia’s borders. Ignoring that makes little military or political sense.