Two rounds of U.S. airstrikes in northwest Syria since September have destroyed bases and weapons depots linked to the al-Qaida-backed Nusra Front, but the more serious damage may have been to the fragile political balance, helping to tip an entire province dominated by pro-Western fighters into the control of al-Qaida, rebel commanders say.

Moderate rebel field commanders, holding emergency meetings in the Turkish border town of Reyhanli as they try to regroup, speak of a popular backlash caused by the bombings that gave Nusra an advantage when it moved against them in Idlib province and forced them to disarm or flee. They voice anger at the United States for attacking Nusra, which has been on the U.S. list of terrorist organizations for nearly two years, without first considering how the action might affect their own battle against the government of President Bashar Assad.

U.S. officials have said the strikes on Sept. 23 and Nov. 6 targeted a group of al-Qaida operatives that American officials call the Khorasan Group, describing them as Arab veterans of the war in Afghanistan whom al-Qaida dispatched to Syria to plot attacks on U.S. and other Western interests. […]