Senior Pentagon officials are defending a 2001 military force law, saying the U.S. remains in armed conflict with al-Qaida and its associate forces.
President Barack Obama has used the law to target terrorists with fatal drone strikes, including on Americans overseas.
The law was enacted days after the 9/11 attacks. Civil libertarians and some lawmakers wonder if it's a blank check for the president, and whether it should be revised to deal with emerging threats.
A Senate panel heard from officials who say the U.S. may defeat the enemy someday, but that is a long way off.
Testifying were acting general counsel Robert Taylor and assistant secretary for special operations Michael Sheehan.
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