Authority of the President to Use Military Force Against ISIL

The rise of the Islamic State of Iraq and the Levant (ISIL) as a territorial entity controlling significant areas of Iraq and Syria posed an unprecedented challenge to existing frameworks for the authorization of military force. ISIL emerged from the remnants of al-Qaeda in Iraq and evolved into an organization that declared a caliphate, controlled territory, maintained a military apparatus, and directed and inspired terrorist attacks against Western targets. The organization's rapid territorial expansion in 2014, including the seizure of Mosul, Iraq's second-largest city, prompted urgent questions about the legal authority for U.S. military action.

The President initiated airstrikes against ISIL in August 2014, citing both his constitutional authority as Commander-in-Chief and the 2001 Authorization for Use of Military Force. Congressional leaders from both parties raised questions about whether the existing statutory authorizations were sufficient or whether new legislation was required. This opinion was requested to provide a comprehensive legal framework for the ongoing military campaign.

The constitutional analysis begins with Article II, Section 2 of the Constitution, which vests the President with the role of Commander-in-Chief of the armed forces. The Supreme Court has recognized that the President has the authority to use military force to protect national security interests, even absent specific congressional authorization, provided the operation does not rise to the level of a "war" within the meaning of the Constitution's allocation of the war-declaring power to Congress. The Office of Legal Counsel has historically applied a two-part test: whether there is a sufficient national interest to justify the use of force, and whether the anticipated nature, scope, and duration of the operations rise to the level of a "war" requiring prior congressional authorization.

Under the 2001 AUMF, Congress authorized the President to use all necessary and appropriate force against those nations, organizations, or persons who planned, authorized, committed, or aided the terrorist attacks of September 11, 2001, or harbored such organizations or persons. The critical legal question is whether ISIL falls within the scope of this authorization, given that the organization split from al-Qaeda's central leadership. The opinion concludes that ISIL's historical origins as al-Qaeda in Iraq, its continued ideological alignment with the broader jihadist movement, and its operational connections to individuals associated with the September 11 attacks provide a sufficient nexus to bring it within the AUMF's reach. The 2002 Iraq AUMF provides additional statutory authority, as ISIL's operations in Iraq implicate the ongoing threat to stability in that country.

The War Powers Resolution requires the President to report to Congress within 48 hours of introducing armed forces into hostilities and to withdraw forces within 60 days absent congressional authorization. The opinion analyzes the President's compliance with these requirements and concludes that the combination of Article II authority and the existing AUMFs satisfies the Resolution's requirements. However, the opinion distinguishes between limited airstrikes and advisory operations, which fall within the President's existing authority, and the deployment of sustained ground combat operations, which would present more significant constitutional questions.

The President possesses constitutional and statutory authority to conduct military operations against ISIL under both Article II of the Constitution and the 2001 and 2002 AUMFs. The scope of permissible operations includes airstrikes, intelligence gathering, logistical support to partner forces, and the deployment of special operations forces for targeted missions. Sustained ground combat operations involving large numbers of U.S. forces in an offensive role would require careful reassessment of the legal framework and potentially new congressional authorization.

This opinion established the legal foundation for Operation Inherent Resolve, the multi-year military campaign against ISIL. It influenced congressional debates about a new AUMF specifically targeting ISIL, though such legislation was never enacted. The opinion's analysis of the scope of the 2001 AUMF contributed to the ongoing expansion of that authorization's reach to cover successor and associated forces, a development that continues to shape executive war powers. Defense counsel and national security practitioners must consider this opinion when advising on the scope of military authority in counterterrorism operations.