Having been drawn this far into the conflict, Washington cannot now accept a Ukrainian defeat without a serious loss of honor and prestige. But even discounting the nuclear risks, the task of assisting a bankrupted Ukraine to prevail against larger Russian forces in a war of attrition is a daunting one. Currently, the Biden administration is committed to winning a war it thought wouldn’t happen on the side of a country it believed to be helpless in the face of dangers and difficulties it does not yet know how to assess…

This change in Western perceptions makes compromise much harder to find. A few weeks ago, appeasing Mr. Putin by feeding him more slices of Ukrainian territory in a “compromise peace” looked to many Western policy makers like the natural and necessary conclusion to the war. That approach now seems both morally repugnant and strategically vain. This changed view explains why Defense Secretary Lloyd Austin and Mrs. Pelosi have begun to speak of degrading Russian power and seeking victory for Ukraine.

This changing Western approach confirms Mr. Putin’s belief that the conflict between Russia and the West over Ukraine is an existential one for Russia. Without Ukraine, Russia cannot truly be a great power, and the West is willing to fight to prevent Russia from achieving what, from Mr. Putin’s perspective, is an indispensable goal.