The Ukrainian military is facing a critical shortage of infantry, leading to exhaustion and diminished morale on the front line, military personnel in the field said this week — a perilous new dynamic for Kyiv nearly two years into the grinding, bloody war with Russia. In interviews across the front line in recent days, nearly a dozen soldiers and commanders told The Washington Post that personnel deficits were their most critical problem now, as Russia has regained the offensive initiative on the battlefield and is stepping up its attacks. One battalion commander in a mechanized brigade fighting in eastern Ukraine...