The other day in Wurzburg, Germany a 17-year-old Afghan refugee boarded a train carrying a knife and ax. Then he went to work. Four passengers -- Chinese tourists -- are in serious condition. Others were less seriously injured. Many aboard the train were treated for shock. The kid’s Lizzie Borden routine was accompanied by his shouts of “Allahu Akbar.” Beforehand, in a video, he had declared himself a soldier of the caliphate. Among his possessions was a homemade flag that resembled an Islamic State banner. German police gunned him down as he attacked security while attempting to flee. The attack,...