In June, the White House authorized the Central Intelligence Agency to help arm moderate fighters battling the Assad regime, a signal to Syrian rebels that the cavalry was coming. Three months later, they are still waiting.

The delay, in part, reflects a broader U.S. approach rarely discussed publicly but that underpins its decision-making, according to former and current U.S. officials: The Obama administration doesn't want to tip the balance in favor of the opposition for fear the outcome may be even worse for U.S. interests...