Defense Secretary James Mattis on Wednesday threw his support behind a new war authorization specific to the fight against the Islamic State in Iraq and Syria (ISIS).

“I would take no issue with the Congress stepping forward" with an authorization for the use of military force, Mattis told the Senate Appropriations defense subcommittee. “I think it'd be a statement of the American people's resolve if you did so. I thought the same thing for the last several years, I might add, and have not understood why the Congress hasn't come forward with this, at least the debate.”

Officials currently cite the 2001 authorization for the use of military force (AUMF) passed in the wake of the 9/11 attacks as their the legal authority to prosecute the fight against ISIS.

That justification has been controversial for some because ISIS did not exist when the AUMF passed. Others say the justification may be legally sound, but passing a new AUMF would send a show of support to troops.

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A new authorization has stalled in Congress for several years.

Former President Obama requested Congress pass a new AUMF in 2015, but the proposal went nowhere as Republicans said it was too restrictive, while Democrats argued it was too broad.

Lawmakers have also introduced various AUMFs in recent years, but they also fell flat over the same arguments.

Asked later in Wednesday’s hearing whether a new AUMF should have time limits, Mattis flatly said no.

He also said geographic constraints would “only work to help the enemy.”

Mattis said, however, that Congress should decide on what means to allow. For example, Congress has fought over whether to allow ground troops.

“I think it would be best if Congress would say what they want us to accomplish ... I have no reservations about sharing in closed session with you how we would carry that out,” he said.

Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford, who was testifying alongside Mattis, also expressed support for a new AUMF.

“I think not only would it be a sign of the American people's resolve,” Dunford said, “but truly I think our men and women would benefit from an authorization for the use of military force that would let them know that the American people, in the form of their Congress, were fully supportive of what they're doing out there every day as they put their lives in harm's way.”