Russia’s defense minister said 200,000 men had entered the army as part of a mobilization drive that began last month as the rapid advance of Ukrainian forces into Russian-occupied territories outpaces Moscow’s ability to pour in reinforcements. The suggestion that Russia is already two-thirds of the way toward the target the minister, Sergei Shoigu, announced last month follows criticism of the call-up process—including from Russian President Vladimir Putin. But it raises questions as to whether the depleted Russian military will be able to cope with the sheer numbers of new recruits and use them effectively. Western military analysts say Moscow...