I would add that overt US intervention might trigger a wave of patriotism in Russia too, and enable Putin to spin the whole thing as a war of survival. Which it very well might be at that point, I for one do not think a No-Fly-Zone -like conflict would stay restricted to Ukraine, or to the sky for that matter. Seen in that light Putins trade off matrix before the war might have looked like a win-win; Either the US doesn’t intervene, and then he can take Ukraine easily: Or, the US does intervene, and then he can blame the capitalist world order. The worst outcome is Ukraine repelling him without the US.
I would add that overt US intervention might trigger a wave of patriotism in Russia too, and enable Putin to spin the whole thing as a war of survival. Which it very well might be at that point, I for one do not think a No-Fly-Zone -like conflict would stay restricted to Ukraine, or to the sky for that matter. Seen in that light Putins trade off matrix before the war might have looked like a win-win; Either the US doesn’t intervene, and then he can take Ukraine easily: Or, the US does intervene, and then he can blame the capitalist world order. The worst outcome is Ukraine repelling him without the US.