President Vladimir V. Putin of Russia has thrust himself more directly into strategic planning for the war in Ukraine in recent weeks, American officials said, including rejecting requests from his commanders on the ground that they be allowed to retreat from the vital southern city of Kherson. A withdrawal from Kherson would allow the Russian military to pull back across the Dnipro River in an orderly way, preserving its equipment and saving the lives of soldiers. But such a retreat would be another humiliating public acknowledgment of Mr. Putin’s failure in the war, and would hand a second major victory...