A little history would help!
"The Bush Administration later sought an agreement with the Iraqi government, and in 2008 George W. Bush signed the U.S.–Iraq Status of Forces Agreement. It included a deadline of 31 December 2011, before which "all the United States Forces shall withdraw from all Iraqi territory".[11][12][13] The last U.S. troops left Iraq on 18 December 2011, in accordance with this agreement.[1][11][12] US Forces, in the form of air support, resumed operations in Iraq in June 2014, to defend it against ISIL"