No longer the unthinkable? Putin repeats nuclear threat as Russia retreats in Ukraine

What happens when the people no longer believe their own leader? With a stroke of the pen, Vladimir Putin annexing Russian-held parts of Ukraine even as those territories shrink in real time. As the casualties mount and amid the blowback against mobilization, what will this Russian president do if he keeps losing on the battlefield? How does a cornered nuclear-armed strongman react?