WASHINGTON — With rebel forces in Syria in retreat and the Obama administration’s policy toward the war-ravaged country in disarray, Secretary of State John Kerry arrived at the White House Situation Room one day in June with a document bearing a warning. President Bashar al-Assad of Syria had used chemical weapons against his people, the document said, and if the United States did not “impose consequences,” Mr. Assad would see it as a “green light for continued CW use.”

President Obama had signed a secret order in April — months earlier than previously reported — authorizing a C.I.A. plan to begin arming the Syrian rebels. But the arms had not been shipped, and the collapse of rebel positions in western Syria fueled the atmosphere of crisis that hung over the June meeting.
Yet after hours of debate in which top advisers considered a range of options, including military strikes and increased support to the rebels, the meeting ended the way so many attempts to define a Syrian strategy had ended in the past, with the president’s aides deeply divided over how to respond to a civil war that had already claimed 100,000 lives.
The State Department’s June warning, laid out in a document obtained by The New York Times, proved to be prophetic. A devastating poison gas attack on Aug. 21 killed hundreds of civilians, touching off a crisis that brought the United States close to launching military strikes in Syria and that ended only when Mr. Obama seized on a Russian-sponsored agreement to secure Syria’s chemical weapons.
Now, two years after Mr. Obama publicly declared that Mr. Assad had to go, he is banking on the success of that Russian-initiated plan — which relies on Mr. Assad’s cooperation and which the Syrian president offered in a recent interview as a convenient shield against American intervention.