NEITHER BA'ATHIST NOR SALAFIST:

More than two months after the campaign against the Islamic State plunged the United States into direct military involvement in Syria, something Mr. Obama had long avoided, the group has held its strongholds there and even expanded its reach. That has called into question basic assumptions of American strategy.

One is that the United States can defeat the Islamic State without taking sides in Syria's civil war. Another is that it can drive the group out of Iraq while merely diminishing and containing it in Syria, pursuing different approaches on each side of a porous border that the Islamic State seeks to erase.

"The fundamental disconnects in U.S. strategy have been exposed and amplified" as Islamic State militants have advanced in central Syria in recent weeks, said Emile Hokayem, a Syria analyst at the International Institute for Strategic Studies. Like Mr. Assad's opponents, he contends that extremists cannot be defeated without ending decades of harsh Assad family rule and empowering the disenfranchised Sunni Muslims who drive the insurgency.

Mr. Obama has sought to treat Syria as a separate problem and concentrate on Iraq, where he sees more compelling United States interests -- if only the political need to salvage the legacy of American deaths there. But most analysts say the two conflicts are inextricable.

In Iraq, the group, also known as ISIS or ISIL, seems to have reached the limits of its expansion as it bumps up against areas without a Sunni Arab majority and Iraqi and Kurdish forces make some gains. But driving it out entirely is another matter, particularly if it can rely on a rear base in Syria, where Mr. Hokayem said it could still expand in majority-Sunni areas.

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