Obama cites authority to fight Islamic State. Why some lawmakers don't buy it.

For the Islamic State fight, President Obama pointed to two authorizations passed by Congress more than a decade ago. Their applicability to today is stirring debate with the force of a Tomahawk missile.

Behind President Obama’s call at the United Nations on Wednesday for the world to help the United States fight the Islamic State (IS) lies the question: What authority does he have to use US military force in this fight?

Mr. Obama referenced it in a letter to the leaders of Congress on Tuesday. He cited his constitutional authority as commander in chief and then, in parentheses, pointed to two authorizations passed by Congress.

But both are more than a decade old. Their applicability to today is stirring debate with the force of a Tomahawk missile.

Officially, each law is referred to as an Authorization for Use of Military Force – or AUMF, an acronym as ugly as its lethal purpose. The first AUMF, in 2001, was passed in the immediate aftermath of the 9/11 attacks. It allowed the president to use “all necessary and appropriate force” against nations, groups, or individuals associated with the attacks, to prevent future attacks. 

The second, passed in 2002, gave the OK for force against Iraq – to enforce UN Security Council resolutions related to Iraq and to “defend” the US against the “continuing threat posed by Iraq.” The following spring, the US invaded Iraq.

In the past, the Obama administration has argued for rescinding both authorizations for being too broad, open-ended, or outdated. Now, as it relies on them, some lawmakers are the ones arguing these points.

The White House's use of old authorizations is an “extremely creative stretch by extremely creative lawyers,” said Sen. Tim Kaine (D) of Virginia, at the liberal Center for American Progress on Tuesday. He and other members of Congress – both Democrat and Republican – say Congress must approve a new authorization specific to IS, also called ISIS or ISIL. He, and others, have already introduced authorizing legislation in both the Senate and House.

Here’s their line of argument. IS is not associated with the perpetrators of the 2001 attacks, so it doesn’t fit under the 2001 AUMF. Indeed, it broke from Al Qaeda. Its goal is to establish a caliphate. If the president uses 2001 authority for something like this, they say, he can skip congressional approval for use of force in the future.

Neither does the 2002 AUMF apply, they say. Saddam Hussein and his supposed weapons of mass destruction are long gone. The aim to “degrade and ultimately destroy” IS, as Obama says he wants to do, is an entirely new effort that requires new congressional authorization – especially since, as the president acknowledged in his letter, “it is not possible to know the duration” of US deployments of military personnel and equipment for this fight, supporters of congressional approval argue.

It's also important, at the start of this endeavor, to build public support through representatives in Congress, they add.

Administration officials counter that IS may have broken from Al Qaeda, but is still at war and in conflict with America. And Antony Blinken, deputy national security adviser, said in an NBC interview Tuesday that this week’s strikes in Syria are justified by “a doctrine of collective self-defense.” Iraq asked the US and other nations to act, because “ISIL in Syria threatens them.”

Congress has an opportunity to craft a new authorization when it convenes a lame-duck session after the midterm elections, if leaders allow such legislation to come to the floor. So far, Obama has not asked for new approval – perhaps fearing he might not get it from a dysfunctional Congress.

One thing could force the issue: money. Congress has the power of the purse; it funds the military. With an ongoing military operation against IS, the president is going to need more money to fund it. And that’s where Congress could have its leverage.