Police and military officers swooped down on a Moscow business center this past week unannounced. They were looking for men to fight in Ukraine — and they seized nearly every one they saw. Some musicians, rehearsing. A courier there to deliver a parcel. A man from a Moscow service agency, very drunk, in his mid-50s, with a walking disability. “I have no idea why they took him,” said Alexei, who, like dozens of others in the office complex, was rounded up and taken to the nearest military enlistment office, part of a harsh new phase in the Russian drive. In...