WASHINGTON (AP) — The Obama administration searched for answers Wednesday about a reported chemical weapons attack in Syria that would mark the most flagrant violation yet of the U.S. “red line” for potential military action. But the possibility of intervention seemed ever smaller after America’s top general offered a starkly pessimistic assessment of options.

Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said in a letter this week to a congressman that the administration is opposed to even limited action in Syria because it believes rebels fighting the Assad government wouldn’t support American interests if they seized power.