When the west tried to swindle Russia out of access to its naval ports in Ukraine, that was the last straw and Russia took Ukraine back [it had been Russian since the time of Catherine the Great]. We will have mutual suicide by nuke before Russia gives up Crimea. It's their vital interest and we have none except to FA with Russia.
This is the core of the European stakes involved in Ukraine. Europe KNOWS that Russia can never give up the Crimea, their only warm water access to the world's oceans AND the key to their status as a global naval power.
IOW, Europe wants Russia defeated - - - but they can't achieve that themselves so they want the Yanks to bankroll the conflict and most likely to carry the burden of supplying troops. Their leverage in order to accomplish this prod against the U.S. is NATO.
Obviously the Trump team has hinted at the possibility of withdrawing the U.S. from NATO. Europe is gambling that the U.S. is just bluffing and convincing Zelensky to hold out against a peace deal. Europe screwed us repeatedly in Ukraine during the Bitem Administration. See my post portraying this.