Tracing Pakistan's role at the heart of the Afghanistan war

The U.S. has been fighting in Afghanistan for more than 16 years, and mostly against the Taliban, a group that exists in large part due to the intelligence services of Afghan neighbor Pakistan. Steve Coll’s new book "Directorate S" is perhaps the definitive story of the war’s aftermath and tense U.S. relations with Pakistan. Coll joins Nick Schifrin for a conversation.