President Obama's decision last weekend to launch U.S. surveillance flights over Syria in preparation for possible airstrikes against the Islamist militants who have overrun large swaths of the country since June has brought the U.S. another step closer to direct involvement in the years-long civil war there. But it still hasn't resolved the most vexing question facing U.S. policymakers: How does one reverse the military gains of the radical Islamic State, which is now menacing Iraq as well, without at the same time strengthening Syrian President Bashar Assad's hold on power?

Ever since the popular uprising against Mr. Assad began in 2011, Mr. Obama has insisted the Syrian dictator must step down. But the administration has done little to hasten that process. Mr. Obama, who campaigned on a pledge to end the wars in Iraq and Afghanistan, is surely aware of polls showing Americans are reluctant to get involved in another messy Middle East conflict. Moreover, the president shared the concerns of his top military advisers that sending weapons and equipment to the moderate Syrian opposition risked seeing them eventually fall into the hands of radical Islamists affiliated with al-Qaida.

Initially, at least, Mr. Obama may have thought that Russia, Mr. Assad's strongest backer, could be persuaded to cooperate in brokering a peace that obliged Mr. Assad to voluntarily give up power. In retrospect, such hopes seem badly misplaced. Russia not only has refused to pressure Mr. Assad into stepping aside but is actively working to strengthen his military. Meanwhile, the radical Islamic State has emerged as the strongest Syrian opposition faction and expanded its operations into Iraq, where it now threatens the Shiite-led government in Baghdad as well as Kurds in the north using U.S. weapons it captured from the Iraqi Army.

Mr. Obama already has authorized U.S. airstrikes against ISIS militants besieging the northern Iraqi city of Irbil. The strikes temporarily succeeded in halting ISIS' advance and allowed Kurdish pesh merga militias to retake some nearby towns previously occupied by the militants. But U.S. officials warn that ISIS is likely to regroup and resume its offensive in Iraq and that the group cannot be decisively defeated unless the U.S. also targets its forces in Syria. So far, Mr. Obama has stuck to his refusal to intervene militarily in Syria's civil war, but events now may be forcing his hand.

There's no question that the U.S. and its allies have the capability to strike ISIS in Syria. The real issue is to what end? Airstrikes alone are unlikely to break the group's determination to fight — witness the failure of the massive Israeli airstrikes in Gaza to stop Hamas-led fighters from continuing to launch rockets against Israeli cities. And Mr. Obama insists that even if he does order airstrikes in Syria, he draws the line at putting American boots on the ground there.

But ISIS can no more be defeated from the air than Hamas, no matter how many tons of ordnance are dropped on it. Sooner or later, Kurdish and Iraqi government forces will have to engage ISIS militants on the ground to clear them from the areas in Iraq they now control.

Whether the Kurdish militias and the Iraqi army are up to that task is unclear. But even if they are that won't solve the conundrum posed by ISIS' presence in Syria, where Mr. Assad is skillfully playing off the radical Islamists against the moderate opposition by encouraging them to fight each other while he husbands his own forces to defeat whichever rebel faction ultimately emerges as victor.

Either way it's hard to see how U.S. airstrikes against ISIS in Syria won't put the Obama administration on a slippery slope toward becoming more deeply involved in that country's civil war, and in a way that forces it to choose between the lesser to two malignant evils, the Islamic State or Mr. Assad. The irony is that's the very nightmare scenario Mr. Obama for so long sought to avoid, but at this point there may be no way around it.


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