"The Islamic State is a transnational Sunni Islamist insurgent and terrorist group that has expanded its control over areas of parts of Iraq and Syria since 2013. It threatens the governments of both countries and potentially several other countries in the region. The emerging international response to the threat is multifaceted and includes coalition military strikes and assistance plans. There is debate over the degree to which the Islamic State organization might represent a direct terrorist threat to the U.S. homeland or to U.S. facilities and personnel in the region. […] The U.S. desire to show progress against the Islamic State and in the recruitment of regional partners raises questions of whether the U.S. mission and commitment might expand. The Administration has ruled out deploying combat forces to either Iraq or Syria, but it has not ruled out providing forward aircraft controllers, additional military advisors, or other related ground-based military assets. Some experts assert that coalition partners inside Iraq and Syria--Iraqi government forces and select Syrian groups--are too weak to defeat the Islamic State and will eventually require help from U.S. combat troops. Several regional coalition members apparently seek an expansion of the U.S.-led mission to include an effort to oust President Asad of Syria."
CRS Report for Congress, R43612