"This is one of the most fundamental divisions in our constitutional scheme that the Congress has the power to declare war. The president is the commander in chief and prosecutes the war," Sen. Angus King (I-Maine) said during Thursday's Senate Armed Services Committee hearing.
Passed in the days immediately after the 9/11 attacks, the authorization law gave military and intelligence agencies wide leeway to pursue al Qaeda.
From the U.S. terror detainee program to armed drone strikes, the rules have allowed American forces to kill most of the terror group’s senior leaders, including Osama bin Laden.
But more than a decade after the law was approved, White House counterterrorism officials have used the law's mandates to expand the scope of those operations far beyond hunting down the perpetrators of 9/11.
That expanded scope, according to King, could let U.S. military and intelligence units conduct combat operations outside the War Powers Act.
The act specifically requires the White House to notify Congress anytime the United States seeks to take military action in a foreign country.
The Obama administration has come under fire for violating the War Powers act by sending American airpower and warships to Libya in 2011 as part of the United Nations peacekeeping operation in the country.
To that end, committee chairman Sen. Carl Levin (D-Mich.) said the panel is drafting a letter to Attorney General Eric Holder, seeking clarification on how the AUMF affects congressional oversight of combat operations under the War Powers act.
"Senator King has raised an extremely important question. It needs to be answered, I believe, in a much more definitive way for the record," by the White House, Levin said.
The rules of war passed by Congress after 9/11 allowed the U.S. "to be at war with al Qaeda," Robert Taylor, the Defense Department's acting general counsel, told committee members Thursday.
"That organization ... has associated forces, forces that have joined with that organization," he said. "And, yes sir, we are authorized to attack ... those who have chosen to associate with that organization."
That interpretation, according to King and others on the panel, opens the door to unilateral military action against alleged affiliates in Syria, Africa, Yemen and elsewhere across the globe.
Al Qaeda cells, such as al Qaeda's Yemeni cell known as al Qaeda in the Arabian Peninsula (AQAP) "is certainly within the scope of the authorization for the use of military force enacted by the Congress," Taylor said.
Those laws "provides the authority to take the fight to AQAP just as it provides the authority to take the fight to al Qaida senior leadership," he added.
To that end, Sen. John McCain (R-Ariz.) asked Taylor if the United States had the authority under AUMF to launch counterterrorism operations in Syria and Mali, given al Qaeda-affiliated groups in those countries.
Taylor replied: "On the domestic law side, yes sir."
The White House blocked U.S. combat troops from going into Mali earlier this year, restricting the Pentagon to a support role for French-led operations against al Qaeda's West African cell, dubbed al Qaeda in the Islamic Magreb (AQIM), in the country.
Later during the hearing, Brig. Gen. Richard Gross, the top legal counsel for the Joint Chiefs of Staff, told the panel that possible U.S. military action against the Syrian-based Jabhat al-Nusra (JAN) would also be covered by the AUMF.
"We'd have the ability to act against al-Nusra. If we felt they were threatening our security, we would have the authority to use that [authority] to do that today," Gross said.
President Obama is still weighing possible military options in Syria, but has largely dismissed the notion of possible U.S. troop deployments to help end the civil war there.
In either instance, the White House could order direct military action in a foreign country without congressional consent, thanks to the wide-ranging interpretation of the AUMF, according to King.
"We may need new [counterterrorism] authority, but ... if you expand this to the extent that you have ... the limitation in the War Powers [Act] is meaningless," he said.