A US congressman will launch a vote as early as Wednesday to repeal the US government’s vastly expanded post 9/11 war powers.

Adam Schiff, a California Democrat, has authored a measure that would force the expiration of the September 2001 Authorization to Use Military Force, or AUMF, the legal wellspring of America's so-called "war on terror", in one year.



The measure, offered as an amendment to the annual defense budget funding authorization, could come for a vote in the House of Representatives as early as Wednesday afternoon.



Schiff offered a similar measure last year that came about 30 votes short of passing the House. He told the Guardian on Wednesday that he was “optimistic” about it passing this time around, thanks to growing bipartisan discontent in Congress as terrorist threats have mutated in the 13 years since the law’s creation.

“There’s been an increasing recognition that the current AUMF is badly out of date and poorly describes the nature of the conflict that we’re in,” Schiff said.

“The current AUMF is tethered to 9/11 and the groups that were responsible, but is nonetheless now being applied to al-Qaida affiliates that weren’t even in existence on 9/11. So you hear Democrats and Republicans in the House and Senate talking about how poorly defined the AUMF is in terms of the current conflict. There’s less consensus about what ought to be done about it.”



The law, crafted to respond to the perpetrators of 9/11, has become the justification used by the Bush and the Obama administrations for everything from indefinite detention at Guantánamo Bay to drone strikes in Yemen to capture raids in Libya. The Obama administration has come to rely on a claim that the AUMF permits military action against “associated forces” of al-Qaida worldwide, even though those words are not found in the 2001 law.



President Obama said in a May 2013 speech he wanted to refine and “ultimately repeal” it, as part of a step to move the US off what he called a “perpetual wartime footing.”



But there has been no progress on constraining or abolishing the AUMF since the speech. During a hearing on Wednesday, administration lawyers received frustration and skepticism from senators of both parties after arguing that the it ought to be repealed – just not quite yet.



“We’re not here today calling for immediate repeal,” Stephen Preston, the senior Pentagon lawyer and a former CIA general counsel, told the Senate foreign relations committee.



Backed by his State Department counterpart Mary McLeod, Preston argued that without the AUMF, the president’s inherent constitutional powers provide sufficient legal cover to take “a series of persistent targeted efforts to dismantle existing violent networks threatening our country” worldwide. He opened the door to expanding the list of al-Qaeda “affiliated” groups, already a global collection.



Those broad claims of presidential wartime authority -- reminiscent of those made by Dick Cheney -- prompted senators to question why they should bother repealing the AUMF at all.



The ranking Republican on the committee, Bob Corker of Tennessee, called Preston and McLeod’s testimony “bizarre” and “not particularly gratifying.” The chairman, Democrat Bob Menendez of New Jersey, said: “I’ve got to get a sense at least from an administration perspective of what the AUMF gave you that you didn’t otherwise have.”



Ron Johnson, a Wisconsin Republican, criticized the administration for not even providing Congress with proposals to amend the AUMF in the year since Obama’s speech. Even Schiff, whose amendment aligns with Obama’s stated goals, said that he had not received specific assistance from the administration on “what ought to follow, or what do you think of this draft.”



“I think the imperative of Fisa [surveillance] reform sucked a lot of oxygen out of the room, on the Hill and in the administration, that was where our primary focus was placed,” Schiff said, predicting that “now we can turn our full attention to the AUMF.”



But lurking behind the AUMF debate is deep administration and congressional uncertainty about the proper scope, after 13 years, of both the threat from al-Qaeda affiliates and the appropriate US response.



“Not every collection of thugs that labels themselves al Qaeda will pose a credible threat to the United States,” Obama contended in his May 2013 speech at the National Defense University.



But a host of intelligence and military officials have testified since that terrorist attacks abroad are growing worse, prompting criticism that the administration has inappropriately narrowed its focus to attacks inside the US. A State Department annual report found that terrorist attacks had surged by 43 percent in 2013, while killing few Americans.



Meanwhile, the killing of four Americans in Benghazi in 2012 by a terrorist group unaffiliated with al-Qaeda and the rise of a potent jihadist faction in Syria – known as ISIS and excommunicated by al-Qaeda – has prompted criticism, largely on the right, that Obama wants to declare an unfinished war prematurely ended, even as the AUMF does not grant him sufficient power to respond to the latest incarnations of terrorism.



But in fending off the claim from conservatives that the president needs the AUMF, the Obama administration has discomfited liberals by claiming vast inherent presidential powers, under Article II of the Constitution, for global military action.



Schiff said he “regrettably” favored Congress passing a new and more limited AUMF, a controversial position among liberals, as a check on presidential power.



“The failure to do so will mean the administration, as it appears it is testifying today, will simply use its authority under Article II. The administration is on its strongest constitutional footing when it acts in concert with Congress,” Schiff said.



Schiff said that a follow-on authority “has to be limited in duration” and “narrowly circumscribed for the nature of threat for force to be used.”