To its critics, President Obama's strategy to combat the Islamic State in Syria and Iraq is weak and incoherent. Even some of the staunchest U.S. allies and partners in the fight worry that the time for what they see as the administration's incremental approach has long since passed. The White House maintains that its strategy is comprehensive and that it's working. Sharp increases in airstrikes and Obama's recent decision to deploy Special Operations troops, officials say, are part of a fundamental change in the military's mission developed this fall, along with a new diplomatic push to end the distraction of...