Running out of time. Source: Stringer/Anadolu Agency via Getty Images
Running out of time. Source: Stringer/Anadolu Agency via Getty Images

The Islamic State in Iraq and the Levant, which just rebranded itself the Islamic State and now controls significant parts of Iraq and Syria, presents the U.S. with both a security threat and a policy dilemma. In Iraq, fighting ISIL means helping the government put down a Sunni rebellion. In Syria, fighting ISIL means helping a Sunni rebellion fight the government.

The only constant here is fighting ISIL. It's this context that best explains President Barack Obama's request to Congress for $500 million to arm and train Syria's opposition. The aid may or may not be a breakthrough in the quest to end Syria's brutal civil war, but it certainly offers the U.S. a way to fight ISIL outside the political complications of Iraq.

Obama's request backs up his pledge last month to "work with Congress to ramp up support" for opposition fighters. It puts the U.S. military, rather than the Central Intelligence Agency, in charge -- thus raising the profile of American involvement and inviting greater congressional oversight. And, critically, it could push back against ISIL.

After two years of lower-level support for the opposition -- including some clandestine training and arming efforts -- the U.S. should be able to identify teams to trust with anti-aircraft missiles to take out the Syrian helicopters and aircraft that have been killing fighters and civilians. U.S. officials worry that such weapons might fall into the hands of terrorists. That risk exists, but no one is talking about passing out Stingers as if they were party favors, as the CIA did with more than 2,000 missiles in Afghanistan.

The fighting between moderate and extremist opposition groups in Syria has until now made it harder for them to take on Syrian dictator Bashar al-Assad. At this point, however, ISIL has grown into a problem at least as large as Assad, the moderate Sunni fighters need U.S. assistance more than ever, and they are in a position to help undermine ISIL's regional ambitions.

Time, regrettably, is on the side of the extremists. In the past two years, since Obama first rejected a full arm-and-train program for moderate rebels, jihadist forces in Syria have multiplied. Already, recent events in Iraq are spilling back into Syria, as rival Sunni Islamist radicals who had been fighting ISIL there switch sides to join the winners.

Iraq's Shiite prime minister, Nouri al-Maliki, frustrated by delays in delivering either U.S. aircraft or airstrikes against ISIL, has turned to Iran and Russia for help, creating the same lineup of forces as for Assad across the border.

No one should be under any illusions, of course, about how challenging the situation remains in Syria. Just as the administration made its announcement, for instance, Syria's opposition disbanded the military command of the Free Syrian Army over corruption allegations.

That means U.S. aid will have to be delivered carefully, and in timely fashion. Congress should act quickly so funding is available on Oct. 1, the start of the new fiscal year. This is the chance for congressional critics who have sniped at the administration for not doing enough to put their votes where their mouths are.

To bring Congress along, the administration will have to explain its plans in greater detail. Perhaps officials are reluctant to discuss what kind of lethal equipment the administration intends to provide. Now, with Congress more involved and the higher stakes that have come with Iraq's near-collapse, that sort of reticence just won't do.

To contact the senior editor responsible for Bloomberg View's editorials: David Shipley at davidshipley@bloomberg.net.