A tale of two AUMFs.

• Author: Golan-Vilella, Robert
• Position: Authorization for use of military force

In June, the jihadist organization now calling itself the Islamic State staged a stunning series of operations to capture large swathes of territory in northern Iraq. In the span of just a few days, the militants seized Mosul and Tikrit and continued marching south. Some observers feared that the Iraqi state itself might collapse completely.

Washington quickly scrambled to try to reverse these gains and bolster the Iraqi government. It sent multiple teams of military advisers to Iraq and positioned more intelligence, surveillance and reconnaissance units in the area. The Department of Defense also announced that it was considering conducting air strikes against the Islamic State in order to break the group's momentum.

Among those in the U.S. government who must have been scrambling in the aftermath of this advance were the Obama administration's lawyers. In a strange turn of events, there were in fact three separate legal rationales that could have potentially served as the basis for using military force in Iraq. The first was the president's power as commander in chief under Article II of the Constitution. The second was the Authorization for Use of Military Force (AUMF) passed in response to the terrorist attacks of September 11, 2001. And the third was the 2002 AUMF that authorized the Iraq War--a war that President Barack Obama had already declared over years before.

At a meeting with congressional leaders in mid-June, Obama reportedly told those present that he did not believe the military options that he was considering required any further congressional authorization. Several senior congressional figures of both parties--including Senate Majority Leader Harry Reid, House Minority Leader Nancy Pelosi and John Thune, the GOP's third-ranking senator--all suggested publicly that they agreed with this assessment. Jack Goldsmith, a Harvard law professor and former head of the Office of Legal Counsel, likewise argued that same month that "the 2002 Iraq AUMF almost certainly authorizes the president to use force today in Iraq."

The two AUMFs and the conflicts they underwrote have played an outsized role in the past thirteen years of American foreign policy. Yet both pieces of legislation have also evolved in deeply problematic ways since their passage. One has served as the basis for a conflict surrounded by such a degree of secrecy that many basic facts concerning its scope remain unknown. The other, passed to authorize a war that many Americans would come to think was over, lapsed into disuse and was overlooked by all but a few--but still stayed on the books, with the potential to provide the legal grounds for a future, renewed war in Iraq. Together they tell a story of dangerous drift.

The 2001 AUMF was passed by both houses of Congress with only a single "no" vote between them on September 14, and signed into law by President George W. Bush on September 18. Its central clause gives the president the power to

use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons. Today, the legislation is understood to authorize force against the Taliban, Al Qaeda and their "associated forces." It has been used as the legal basis for the war in Afghanistan, the continued detention of prisoners at Guantanamo Bay, and the targeted-killing campaign that the United States has conducted in Pakistan, Yemen and elsewhere.

The Obama administration's public statements on the scope of the 2001 AUMF have often been vague, but they suggest that its interpretation of the law is quite expansive. At a May 16, 2013, hearing of the Senate Armed Services Committee, Senator John McCain asked Robert Taylor, the acting general counsel of the Department of Defense, whether the AUMF could "be read to authorize lethal force against al Qaeda's associated forces in additional countries where they are now present, such as Somalia, Libya, and Syria." Taylor replied, "On the domestic law side, yes." At the same hearing, Senator Lindsey Graham asked if the president had the authority to "put boots on the ground" in Yemen or the Congo, and Michael Sheehan, the assistant secretary of defense for special operations and low-intensity conflict, answered, "Yes, sir." Sheehan later attempted to revise this answer, saying, "When I said that he did have the authority to put boots on the ground in Yemen or in the Congo, I was not necessarily referring to that under the AUMF." But he never stated explicitly that the AUMF would not provide the president with that authority, or clarified what the alternative...