It is a curious thing when a superpower begins to run out of the two things it needs most in war: fuel and men. Yet that is precisely what seems to be happening to Russia in Ukraine. After more than two years of fighting, Moscow’s once-vaunted war machine is showing unmistakable signs of exhaustion. When Russia launched its invasion in February 2022, it relied heavily on professional soldiers but the disastrous battles outside Kyiv and Kharkiv shattered that backbone. Thousands of seasoned fighters were lost, and the logistical chaos that followed forced Russia into an embarrassing retreat from northern Ukraine....