Polling supports the sense that the U.S. public is reluctant to get involved in a shooting war in Europe over a country few Americans can find on a map. Russia and the United States both are nuclear powers, adding to fears of escalation.

But Biden’s position also raises the question: Would Putin have made different calculations in Ukraine this week if Biden had raised the possibility he would deploy American troops? Or should Biden have stayed mum about what he’d do — adopting a strategically ambiguous position that could have deterred Putin?

Critics of Biden’s stance say it’s impossible to assess exactly what alternative history might have transpired had Biden kept alive the military option. Putin has, after all, had a presence inside Ukraine since 2014, when he first invaded, and he appears intent on taking more of the country.

But the Russian leader’s takeaway from Biden’s unwillingness to deploy troops is that he can get away with a lot, some critics argue, and China is learning the same as it weighs how to deal with Taiwan.