An immediate response was ruled out, however, as the administration sent Congress a draft resolution authorizing the use of force in Syria, even though that is likely to entail an ugly debate involving attacks on the administration’s policies and credibility from the political left and the right.

But acting now and alone — the U.K. has dropped out of any coalition of the willing, and the United Nations is calling for delay — would have been worse. There is lingering resentment about Obama’s stretching of the interpretation of the executive’s war powers and brushing aside Congress in the campaign to topple Muammar Qaddafi in Libya in 2011. An NBC News poll published Aug. 30 found that almost 80 percent of the public wanted congressional approval for any military action in Syria.

Obama also is a victim of his own rhetoric. He first drew a “red line” last year, vowing that any use of weapons of mass destruction by Bashar al-Assad would be unacceptable. It seems clear, say lawmakers who’ve been briefed, that Assad ordered the most recent attack, and it wasn’t the first. Critics of intervention are now asking, if we strike now, what do we do when Assad does it again?