David Petraeus speaks in Los Angeles on Nov. 7, 2014. The former head of the U.S.-led coalition in Iraq tells The Washington Post that Iran and Shiite-backed militias pose a greater threat to Iraq than the self-described Islamic State. Imeh Akpanudosen/Getty Images hide caption

itoggle caption Imeh Akpanudosen/Getty Images

Then-CIA Director David Petraeus testifies on worldwide threats before the Senate Select Committee on Intelligence, on Jan. 31. Zhang Jun/Xinhua /Landov hide caption

itoggle caption Zhang Jun/Xinhua /Landov

Gen. David Petraeus in Kandahar, Afghanistan, on July 4, 2011. U.S. Navy Lt. j.g. Haraz N. Ghanbari/Getty Images hide caption

itoggle caption U.S. Navy Lt. j.g. Haraz N. Ghanbari/Getty Images

Three Afghan men on a motorcycle passed by as U.S. Marines patrolled last month in Afghanistan's Helmand Province. Adek Berry /AFP/Getty Images hide caption

itoggle caption Adek Berry /AFP/Getty Images