Neither the George W. Bush nor Barack Obama White House ever laid out a vision for what an end to the war on terrorism would actually look like. But as Obama prepares for his second term in office, one of his top defense officials is arguing that there is an end in sight, and laying out conditions for when the U.S. will reach it.

"On the present course, there will come a tipping point," Jeh Johnson, the Pentagon's top lawyer, told the Oxford Union in the U.K. on Friday, "a tipping point at which so many of the leaders and operatives of al-Qaida and its affiliates have been killed or captured, and the group is no longer able to attempt or launch a strategic attack against the United States, such that al-Qaida as we know it, the organization that our Congress authorized the military to pursue in 2001, has been effectively destroyed." At that point, "our efforts should no longer be considered an armed conflict."

Johnson's description of the endgame raises more questions than answers. But under his formulation, the 2001 Authorization to Use Military Force (AUMF), which the Obama administration has cited as the foundation of its wartime powers, would expire. That would mean any detainee at Guantanamo Bay who hasn't been charged with a crime would be free to go, although Johnson says that wouldn't necessarily happen immediately. It would also raise questions about whether the U.S. would possess residual legal authorities for its lethal drone program – which Johnson defended to the BBC on Thursday – including the legal basis for any "postwar" drone strike the CIA might perform.

In Johnson's view, once al-Qaida's ability to launch a strategic attack is gone, so too is the war. What will remain is a "counterterrorism effort" against the "individuals who are the scattered remnants" of the organization or even unaffiliated terrorists. "The law enforcement and intelligence resources of our government are principally responsible" for dealing with them, Johnson said, according to the text of his speech, with "military assets in reserve" for an imminent threat.

Johnson, considered one of the more liberal voices on Obama's senior national security team, notably did not say when the U.S. will reach his tipping point. And his vague argument is more likely to provoke debate than settle any legal or strategic questions about the war. But it comes at an auspicious time: just before Obama's second term, when there are visible stirrings in Congress to finally close Guantanamo Bay and accelerate an end to the Afghanistan war. Johnson, according to Foreign Policy's Kevin Baron, is also under consideration to become attorney general, a post from which he'd have greater influence to conclude the war. It's also notable that Johnson's current boss, Defense Secretary Leon Panetta, recently backed away from his earlier rhetoric that the war is abating and heralded its spread to new battlefields in Africa.

Johnson's not a commander. He's the Pentagon's general counsel, meaning his most direct involvement in the war on terrorism surrounds the military's ability to detain suspected terrorists during the conflict. In his view, once the conflict ends, Guantanamo Bays doors have to swing open. Just maybe not immediately.

"In general, the military's authority to detain ends with the 'cessation of active hostilities'," Johnson said. But he pointedly noted that both the U.S. and U.K. governments "delayed the release of some Nazi German prisoners of war" after World War II ended. Still, that would mean the vast majority of Guantanamo's 166 detainees, those who haven't been charged with any crime, would be ultimately free to go – a position almost guaranteed to spark controversy.

Murkier still is what it would mean for intelligence and law enforcement to target the "scattered remnants" of al-Qaida. Most significantly, once the AUMF expires, big questions would immediately arise about the legal framework for the apparatus of drone strikes and commando raids that President Obama has expanded and institutionalized for the long haul. The CIA in particular is a question mark: since the legal rationale for its drone program has never been disclosed, its dependency on the AUMF or its typical "Title 50" authorities is unclear.

Either way, it sets up a broader Constitutional question for targeting Johnson's "scattered remnants" of al-Qaida. "You would then have to consider the scope of the president's Constitutional authority if you didn't have statutory authorization to use force against hostile parties," says Benjamin Powell, a former attorney for the U.S. director of national intelligence. (Who, to be clear, was speaking generically and not about any particular program.) "Some in the administration have taken the position prior to joining the administration that such authority is fairly narrow."

Most provocatively, even though Johnson doesn't offer an opinion about when the U.S. will reach his tipping point for ending the war, an argument can be made that it already has, or at least come close.

al-Qaida's senior leadership has not succeeded in launching a major attack against the U.S. since 9/11. The U.S. drone attacks against its tribal Pakistani havens has abated: a strike on Friday that killed three was the first in over a month. al-Qaida's most active affiliate, based in Yemen, has failed in its major 2009 and 2010 attempts to strike the U.S., and appears not to have launched follow-ups as U.S. commandos and Yemeni forces have intensified their campaign against the group. It's not clear what sort of involvement al-Qaida's northern African affiliate had to the September attack on the U.S. consulate in Benghazi, nor if the assault would constitute the "strategic attack" Johnson defined as al-Qaida's hallmark.

Johnson and his staff didn't respond to questions about the speech. But if he stays on in a second Obama term, it might herald an effort to finally bring more than a decade of war to a close.

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