For one thing, the administration has in no uncertain terms repeatedly declared the conflict in Iraq to be over—and in 2011, the United States effectively pulled out of the country after an agreement to leave a more robust U.S. presence couldn’t be reached with the Iraqi government. That means the White House may no longer be able to seek legal cover by invoking the 2002 law passed by Congress that authorized the Iraq invasion.

“It’s a bad argument,” said Bobby Chesney, an expert on national security law at the University of Texas. “Obviously, the context was for action against the government of Iraq.”

Chesney conceded that the law was used for years afterward to justify continued U.S. operations in the country after Saddam Hussein’s regime fell, but, he said, “We’ve been out for years. To go in there and attack ISIS—it’s really a fresh fight.”

Moreover, the administration has come out in favor of repealing the Iraq Authorization of Military Force—and Obama reiterated last week that he hasn’t changed his mind. That makes asserting it now, at best, inconvenient and at worst, highly hypocritical.

The White House could instead invoke the broader 2001 AUMF that authorized U.S. action against al-Qaida in the wake of the 9/11 attacks. The main problem with that? Al-Qaida leader Ayman al-Zawahiri has denounced ISIS for its conduct in Syria, where it has clashed with an al-Qaida backed group.

In addition, Chesney noted, the 9/11 AUMF was intended to warrant preemptive action against threats to the United States—and there has been little evidence that ISIS has America on its mind. The best thing for the administration’s legal position, he joked, is if al-Zawahiri issues a press release praising ISIS and hinting at reconciliation.

Ahem. Obama ordered military action against Moammar Qaddafi under the questionable “responsibility to protect” paradigm, which actually targeted the government of another country. That’s called “war,” in any other context, and yet not only did Obama not have authorization to conduct war against Libya, he never bothered to seek it after the expiration of the War Powers loophole the White House claimed for legitimization, either.

In this case, the R2P seems much less legally fraught. We are not going to war with the legitimate and recognized government of Iraq, but protecting it against a sack of its capital. And now our nominal ally in Iraq has formally requested the assistance, which allows for executive action. While James Oliphant notes that the WPA proviso about “clear and present danger to the security of the United States” may not be entirely clear with regard to ISIS, it’s also clear from intelligence reports that this group intends to conduct operations against the West at some point.

The time may be propitious for an attack on ISIS, which may have lost some momentum already:

Islamic militants attacked Iraq’s largest oil refinery late Tuesday, but were repelled by Iraqi security forces after an overnight battle, Iraqi officials said Wednesday.

The al Qaeda splinter group known as the Islamic State of Iraq and Syria (ISIS) began their attack late Tuesday night, but fighting continued into Wednesday morning. There were unconfirmed reports that the militants had managed to gain control of much of the refinery compound, but in messages posted on their Facebook page, the Iraqi Special Operations force vehemently denied the claims.

Iraqi special forces, backed up by air support, destroyed an ISIS convoy and gunned down three ISIS snipers during a failed attempt by the group to break into the Baiji refinery, according to the special operations force, part of Iraq’s Interior Ministry which is in charge of security across the country.

Chief military spokesman, Lt. Gen. Qassim al-Moussawi, later said government forces had repelled the attack and that 40 attackers were killed in fighting.

Operations at the sprawling complex were halted and its foreign staff evacuated on Tuesday shut down due to the threat.

This is probably an easy call for Obama to make. Air strikes are a lot more antiseptic than putting ground troops in harm’s way, and a lot more practical in terms of politics, logistics, and timing. It gives Obama a chance to take some action that will at least address the deep concerns from allies in the region about the lack of action and direction from Washington these days, too. Air strikes will also provide a positive impact on the situation and give Baghdad some room to maneuver politically and militarily. Plus, Congress is likely to rally around this limited intervention, which would provide Obama with political cover — if he’s smart enough to seek it. He didn’t in Libya and is still paying the political price for high-handing Congress and going it alone.