That didn’t take long. Less than a day after the U.S. military announced its Spring offensive against ISIS, seasoned military officers said the plan was unworkable. Skepticism about the U.S. and Iraqi military plans for the next phase of the ISIS war begins inside the Pentagon. Less than 24 hours after U.S. military officials publicly detailed their plans for a spring offensive on ISIS-held Mosul, Iraq’s second largest city, many within the Pentagon privately questioned whether that timetable was plausible. They said that they were dubious that their partners in the Iraqi military—the troops supposed to lead the offensive—would be...