Defense Secretary Jim Mattis and Secretary of State Rex Tillerson told the Senate on Monday that the Trump administration is open to Congress passing a new war authorization, but wants no time or geographic limits on fighting terrorist groups.

They echoed an earlier administration assessment in testimony to the Senate Foreign Relations committee, saying Trump has all the legal authority needed to globally pursue the Islamic State, al Qaeda and other groups under authorizations passed by Congress in 2001 and 2002.

The Senate heard testimony from Mattis and Tillerson as it again considers whether to replace the existing authorizations for the use of military force, called AUMFs, in the wake of a deadly ambush on U.S. troops in Niger.

“We cannot put a firm timeline on conflict against an adaptive enemy who would hope that we haven’t the will to fight as long as necessary,” according to Mattis’ prepared remarks. “Instead, we must recognize that we are in an era of frequent skirmishing, and we are more likely to end this fight sooner if we don’t tell our adversary the day we intend to stop fighting.”

The Islamic State and other terror groups also do not adhere to borders or geographic boundaries, so such limits in an AUMF would hamper the military’s ability to react, Mattis said.

Still, he told Congress that an updated version of the war authorization legislation, which has provided the legal basis for the past three administration’s counter-terror war, could send an important message.

“Any new congressional expression of unity, whether or not an AUMF, would present a strong statement to the world of America’s determination,” Mattis said.