Almost all of the federal government's actions against terrorism -- from drone strikes to the prison at Guantanamo Bay -- are authorized by a single law: the Authorization for Use of Military Force.
Congress passed it just after the terrorist attacks of Sept. 11, 2001. Now, President Obama says he wants to revise the law, and ultimately repeal it.
The AUMF is one of the most unusual laws Congress has passed this century. It's less than a page long. The vote was nearly unanimous. And it went from concept to law in exactly one week.
It authorizes the president to go after the groups that planned, authorized, committed or aided the Sept. 11 attacks, or any groups and countries that harbored them. In broad terms, it justified invading Afghanistan. But two presidents have applied it around the world.
"It was vast in the powers that it gave," says Karen Greenberg, who runs the Center on National Security at Fordham Law School. "And it was somewhat vast in its definition of the enemy. However, in many ways, that definition has expanded in the interim years."
Presidents Bush and Obama have used AUMF authority to kill terrorists in Somalia, Yemen and other places far from the Afghan battlefield.
But last week at the National Defense University, Obama said the law needs to change. He explained that after 12 years, the Afghan war is ending, and al-Qaida's core is a shell of its former self.
"Unless we discipline our thinking, our definitions, our actions, we may be drawn into more wars we don't need to fight," the president said, "or continue to grant presidents unbound powers more suited for traditional armed conflicts between nation-states."
Obama promised to work with Congress to refine, and ultimately repeal, the AUMF's mandate.
"And I will not sign laws designed to expand this mandate further," he said.
According to a senior White House official, that threat was a specific reaction to lawmakers who have talked about expanding the law.
Until now, presidents have interpreted a very vague law to give them very broad powers. Sen. John McCain, R-Ariz., has expressed interest in making the law less vague, and making those broad powers explicit.
"Wouldn't it be helpful to the Department of Defense and the American people if we updated the AUMF to make it more explicitly consistent with the realities today, which are dramatically different [than] they were on that fateful day in New York?" he said at a Senate Armed Services Committee hearing earlier this month.
But the White House is moving in the opposite direction.
As a senior White House official put it: "The AUMF should apply to al-Qaida. As we defeat al-Qaida, we should ultimately repeal the law."
As other terrorist groups become threats, the White House believes a president should ask Congress for permission to target those groups on a case-by-case basis.
James Jeffrey, who was deputy national security adviser to Bush, worries about rolling back the law.
"This law has served us well for over a decade," he says. "Much hangs from it, including the detention capability and the ability to use the U.S. military against clear and present dangers to the United States."
That detention piece of the puzzle is key: The Guantanamo prison operates under the AUMF, so repealing this law is also part of the White House's effort to close the prison.
Many in Congress want to keep the prison open. That's one reason this issue will not be easily resolved, says Thomas Kean, who co-chaired the 9/11 Commission.
"I think it'll be a long debate, and it should be," Kean says. "[These are] very, very contentious issues, but the one thing you have to have, I think, in the United States, particularly for something lasting as long as this, is a framework of laws. We're a nation of laws. You can't just do ad hoc as we have in the past."
It's pretty unusual for a president to ask Congress to take away some of his power. But Kate Martin of the Center for National Security Studies says if you look at it a different way, this situation doesn't seem so strange.
"It's not unusual for presidents to end wars, right?" she says. "And if what we were talking about was ending military operations, that would not look like a president giving up power. It would look like a president ending wars."
In fact, the White House wants to change this law authorizing the war on terrorism at the same time the Afghan war ends in 2014. That means it has a year and a half to wrestle with Congress over the details.
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