A five-week campaign of U.S. airstrikes against Islamic State militants in Iraq has forced them to conceal their movements and blunted their acquisition of territory, U.S. officials said. However, the reaction of the group’s fighters—moving and living in more stealthy ways—also makes them harder to target. As military officials prepare to expand the campaign, initial intelligence reports point to noticeable effects in arresting the progress of the militants, while questions remain about whether airstrikes can ultimately succeed in rolling back the group. The U.S. strikes have prevented Islamic State militants from massing large formations of fighters and have exerted pressure on checkpoints the group has tried to operate. The expanded strikes also make it difficult for the group to operate convoys, forcing them to move ammunition and equipment more surreptitiously, the U.S. officials said. Since the airstrikes began in early August, the group has curbed its open use of […]