The meaning of Ukraine’s strike in Kharkiv — and Russia’s retreat

What unfolded on the battlefield of Kharkiv oblast in recent days was a remarkable turning point in Ukraine’s desperate battle to resist Russia’s invasion. A more agile force chased a lumbering army into retreat. The war is not over by any means, but the counteroffensive in Kharkiv has exposed anew Russian President Vladimir Putin’s catastrophic miscalculations that Ukraine would collapse, that it would surrender, that it would be steamrolled by Russia’s massive armor. Not so.

Russia apparently figured the next battle would be for Kherson, to the south, and redeployed forces in...