Here's the thing: We are all part of NATO. Accordingly, if any NATO country is attacked, all NATO members are bound to fight for the attacked country including and especially the U.S.
But the war in Ukraine is a EUROPEAN thing. It is not a NATO thing. No NATO country has been attacked or credibly threatened. For this reason, many Americans believe that the conflict is one that Europe should resolve and pay for, while the U.S. just helps to facilitate the resolution.
Our Beloved President seems to take that view. We are willing to sell military stuff to Ukraine, not to provide such stuff. And the European countries agree. They have recently announced loans to Ukraine of almost a hundred billion US$.