ISIS would likely welcome deeper involvement from the IRGC.During the second Iraq war, Iran's Islamic Revolutionary Guard Corps was one of the United States' fiercest foes. The IRGC was responsible not only for organizing, training and equipping Shiite militants who fought U.S. troops, but also for manufacturing and importing into Iraq so-called explosively formed penetrators, or EFPs, one of the chief banes of American forces there. Also courtesy of Tehran: mortar and rocket attacks on the Green Zone in Baghdad, designed to speed the American departure.
For this reason, in addition to the deep distrust that has characterized U.S.-Iran relations since 1979, it is more than passing strange to hear both American and Iranian officials mooting the possibility of U.S.-Iran cooperation in Iraq today. The U.S. and Iran share an interest in preventing further advances by the extremist Sunni militia that calls itself the Islamic State in Iraq and al-Sham, or ISIS. Nevertheless, accepting Iran's offer of assistance in Iraq would be a grave mistake.