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 than the current stalemate…

Pentagon planners were instructed not to offer strike options that could help drive Mr. Assad from power: “The big concern is the wrong groups in the opposition would be able to take advantage of it,” a senior military officer said. The CIA declined to comment.

The White House wants to strengthen the opposition but doesn’t want it to prevail, according to people who attended closed-door briefings by top administration officials over the past week. The administration doesn’t want U.S. airstrikes, for example, tipping the balance of the conflict because it fears Islamists will fill the void if the Assad regime falls, according to briefing participants, which included lawmakers and their aides.