Iran has drawn its cards from a full deck of Iraqi militias. Abu Mahdi al-Muhandis, who allegedly helped plan the 1983 attack on the U.S. Embassy in Kuwait, now directs the IRGC-backed insurgent group known as Kataib Hezbollah. Qais al-Khazali, charged with kidnapping and killing U.S. Marines in Karbala in 2007, runs an IRGC-allied insurgent group known as Asaib al-Haq, or the League of the Righteous. A third Iraqi Shiite militia is known as the Promised Day Brigades. At Iran’s covert direction, fighters from all three militias have been sent to Syria to battle Sunni rebels there.

Iran allegedly has been able to use Iraq as a staging ground for operations to support Syrian President Bashar al-Assad thanks partly to Hadi al-Ameri, the Iraqi minister of transportation. He headed the Badr Brigade, a pro-Iranian militia.

The sectarian cleavage in Iraq has widened since the United States departed. With Iraqi Shiites pulled toward Iran, Sunnis were drawn back toward the jihadist orbit — especially after Syria lurched into civil war. Al-Qaeda fighters relentlessly moved across the porous border and last year proclaimed themselves the Islamic State of Iraq and Syria. This new jihadist magnet has drawn about 10,000 foreign fighters, many with European passports.