Commercially available quadcopter drones carrying small amounts of explosives are “the most concerning tactical development since the rise of the improvised explosive device in Iraq,” U.S. Marine Gen. Kenneth McKenzie Jr., senior U.S. commander for the Middle East, said last February. But now drones are political weapons as well, and it will get worse. Two weeks ago three quadcopters flew into the heavily fortified ‘Green Zone’ in Baghdad to attack the home of Iraqi Prime Minister Mustafa al-Kadhimi, who won last month’s national election and is working to form a new coalition government. Two of the drones were shot down,...