It would take a lot.
“The Russian establishment, and most ordinary Russians, for their part believe that holding Crimea is vital to Russian identity and Russia’s position as a great power. As a Russian liberal acquaintance (and no admirer of Putin) told me, “In the last resort, America would use nuclear weapons to save Hawaii and Pearl Harbor, and if we have to, we should use them to save Crimea.”
https://quincyinst.org/2023/02/10/crimea-is-a-powder-keg/
Thanks for perspective. Food for thought indeed.