Likewise the Russian side, which has become disabused of easy victory and recognizes the degree of NATO commitment, has felt the ground shifting. To return to a theme, it becomes increasingly conceivable Mr. Putin would prefer being stopped by the Western alliance, with its acknowledged superiority in conventional air power, rather than by Ukraine, which would only dramatize the hollowness, corruption and lack of motivation of the Russian army and paint an unacceptable contrast between the two regimes.

Hold on to your hat. If Mr. Putin wants to draw NATO into the war, he knows how to do it. Chief of the General Staff Valery Gerasimov, one of the war’s three authors along with Mr. Putin and Defense Minister Sergei Shoigu, made an unusual visit to the front lines last week. Presumably he went to see for himself the state of his army. What conclusions did he draw, especially about its ability to hold territory against a Ukrainian counteroffensive in coming months fortified by a large influx of Western equipment?