In October, four American soldiers were ambushed by militants in a remote desert in Niger. What were they doing in Africa, and who were they fighting? It was all part of a shadowy war going back to the attacks of Sept. 11, 2001.  Guests: Alan Blinder, a national reporter for The New York Times; Rukmini Callimachi, who covers terrorism and the Islamic State for The Times. For more information on today’s episode, visit nytimes.com/thedaily.