Why Yemen’s political implosion is dangerous for the U.S.

Yemen's government collapsed Thursday as the U.S.-backed President Abed Rabbo Mansour Hadi and cabinet stepped down, allowing Shiite rebels to effectively take over the capital. Gwen Ifill talks to Gregory Johnsen, author of , "The Last Refuge: Yemen, al-Qaeda, and America's War in Arabia" about the roots of the “slow-motion” collapse and what it means for Western counterterrorism efforts.