Ukrainian leaders have vowed to retake all territory occupied by Russia, prompting a debate over what would be necessary for Ukraine to win and evict Moscow’s forces. The answer is primarily military because Russia is only going to abandon its hard-won gains if its troops suffer catastrophic losses, military strategists say. Behind those talks about weapons and ammunition is a deeper political question as Ukraine’s battlefield fortunes rely heavily on the willingness of Western governments to continue their multibillion-dollar military assistance to Kyiv. And pushing Russian forces out of the entrenched positions they hold in more than 15% of Ukraine’s...