Russia will use nukes because Russians are not a rational race. They are fatalistic. The worst thing you can conceive is what they will do. They cannot be reasoned with and have no intention of being productive, collaborative members of the world community. Anyone thinking they're just threatening without intent to do it don't understand the Russian mindset. They will do it. 100%. They've already been humiliated on the battlefield, and face more of the same. But to back down is weak. They're committed and now so are we. If I were Biden, I'd order U.S. troops to garrison in Ukraine. Dare the Russians to fire on us and let's get on with it.