WASHINGTON -- Confronted with evidence that chemical weapons have been used in Syria, President Obama now finds himself in a geopolitical box, his credibility at stake with frustratingly few good options.
The origins of this dilemma can be traced in large part to a weekend last August, when alarming intelligence reports suggested the besieged Syrian government might be preparing to use chemical weapons. After months of keeping a distance from the conflict, Mr. Obama felt he had to become more directly engaged.
In a frenetic series of meetings, the White House devised a 48-hour plan to deter President Bashar al-Assad of Syria by using intermediaries like Russia and Iran to send a message that one official summarized as, "Are you crazy?" But when Mr. Obama emerged to issue the public version of the warning, he went further than many aides realized he would.
Moving or using large quantities of chemical weapons would cross a "red line" and "change my calculus," the president declared in response to a question at a news conference, to the surprise of some of the advisers who had attended the weekend meetings and wondered where the "red line" came from. With such an evocative phrase, the president had defined his policy in a way some advisers wish they could take back.
"The idea was to put a chill into the Assad regime without actually trapping the president into any predetermined action," said one senior official, who, like others, discussed the internal debate on the condition of anonymity. But "what the president said in August was unscripted," another official said. Mr. Obama was thinking of a chemical attack that would cause mass fatalities, not relatively small-scale episodes like those now being investigated, except the "nuance got completely dropped."
As a result, the president seems to be moving closer to providing lethal assistance to the Syrian rebels, even though he rejected such a policy just months ago. American officials have even discussed with European allies the prospect of airstrikes to take out Syrian air defenses, airplanes and missile delivery systems, if government use of chemical weapons is confirmed.
An Israeli airstrike in Syria on Thursday, apparently targeting advanced missiles bound for the Shiite Lebanese militant group Hezbollah, highlighted the volatile situation. With Syrians already dying by the thousands from conventional weapons, Mr. Obama now confronts the most urgent foreign policy issue of his second term, one in which he must weigh humanitarian impulses against the risk to American lives. After about two years of ineffectual diplomacy, whether or how he chooses to follow through on his warning about chemical weapons could shape his remaining time in office.
The evolution of the "red line" and the nine months that followed underscore the improvisational nature of Mr. Obama's approach to one of the most vexing crises in the world, all the more striking for a president who relishes precision. Palpably reluctant to become entangled in another war in the Middle East, and well aware that most Americans oppose military action, the president has deliberately not explained what his "red line" actually is or how it would change his calculus.
"I'm not convinced it was thought through," said Barry Pavel, a former defense policy adviser to Mr. Obama who is now at the Atlantic Council. "I'm worried about the broader damage to U.S. credibility if we make a statement and then come back with lawyerly language to get around it."
While Mr. Pavel favors a more active response to the killings in Syria, others worry that Mr. Obama may have trapped himself into going too far. Zbigniew Brzezinski, a national security adviser under President Jimmy Carter, told Bloomberg Television that military involvement in Syria would risk "a large-scale disaster for the United States."
Further complicating the president's choices is the murky nature of the evidence against Syria, a constant concern because of the lingering memories of mistaken intelligence on Iraq's weapons a decade ago. American intelligence agencies have medium to high confidence that chemical weapons have been used in Syria, but it is not completely clear who was using them.
The Obama administration recognizes that the rebels and their supporters have an incentive to assume or even exaggerate the use of such weapons because it may be the one thing that could draw in direct Western military intervention against Mr. Assad. The rebels have access to information online about the effects of the weapons, so they may know what symptoms to describe to make their claims seem real.
That makes physical samples crucial -- a challenge in a chaotic environment of conflict where there are few functioning health facilities and little reliable electricity, not to mention roads that are often impassable because of the danger of attacks. Still, residents in areas of suspected attacks have collected evidence like urine, soil, dead birds and hair. In one case, a local group dug up the corpse of a man to remove head and nose hair and place it in plastic vials, then posted a video of the process online.
Yet in turning the matter into an international "CSI" case, Mr. Obama may have set a standard of evidence that could never be met.
While concerns about Syria's chemical arsenal go back years, apprehension rose sharply last July when American intelligence agencies detected signs that the Assad government was moving part of its huge stockpile out of storage. There was some evidence that the Syrian military was mixing chemicals, a possible indication that they were being prepared for use.
The reports grew more disturbing, if still fragmentary, by the weekend of Aug. 18 and 19. Denis McDonough, then the president's principal deputy national security adviser and now the White House chief of staff, coordinated a series of urgent classified meetings in the West Wing. "It was a catalyzing event," said one official involved.
The advisers reviewed an array of pre-emptive military options and quickly discounted them as impractical. The evidence was not strong enough to warrant a pre-emptive strike, they concluded, and military officers said the best they could do with airstrikes or commando operations would be to limit the use of chemical weapons already deployed.
Mr. Obama's advisers also raised legal issues. "How can we attack another country unless it's in self-defense and with no Security Council resolution?" another official said, referring to United Nations authorization. "If he drops sarin on his own people, what's that got to do with us?"
But they concluded that drawing a firm line might deter Mr. Assad. In addition to secret messages relayed through Russia, Iran and other governments, they decided that the president would publicly address the matter.
Several officials said they recalled no discussion about the "red line" phrase but suspected that it came out of the election-year conversation about Iran and how far to allow its nuclear program to progress before being forced to take action. It was a concept that was "embedded in people's prefrontal cortex," one of the officials said.
While surprised at the president's use of the term in regard to Syria on Aug. 20, advisers concluded that it had succeeded, at least for a while, since months passed with no chemical weapons attack.
But then in December, American intelligence agencies detected substantial movement of stores of chemical weapons. The Syrians seemed to be consolidating the weapons into fewer locations, presumably a way of securing them. There were also signs that they were mixing chemicals, which caused "a hell of a lot of concern" in the White House, as one official put it.
On Dec. 23, seven people were reported killed and about 50 were hospitalized in Homs Province from what doctors said was poisonous gas inhalation after an attack apparently by forces loyal to Mr. Assad, but Western officials had difficulty confirming it. An Israeli military official said the casualties seemed to be "tests of the world's reaction."
American and Israeli officials discussed contingency plans for military action but held off, with the Israelis concerned that it would bolster Mr. Assad if foreigners attacked his country, especially Israelis.
If it was a test, another one came on March 19, with attacks in a village west of Aleppo and in a suburb of Damascus. As many as 10 were reported killed in the Aleppo-area attack and about 15 outside Damascus, and 150 others were sickened. Patients described shortness of breath, dilated pupils, convulsions and severe headaches.
The government blamed the rebels for the attack near Aleppo. The rebels, in turn, blamed the government for both episodes. Despite Mr. Obama's outreach to Russia, Moscow joined Mr. Assad in accusing the rebels.
A 'Game Changer'
By chance, Mr. Obama was visiting Israel and, standing next to Prime Minister Benjamin Netanyahu the next day, he declared that "the use of chemical weapons is a game changer," reiterating his August threat. But the White House was not eager to take action, so when the British and French sent a letter to the United Nations seeking an investigation, the Obama administration embraced the effort.
Within days, an Israeli intelligence official presented PowerPoint slides and gruesome photographs at a security conference in Tel Aviv to make the case that Syrian forces had used chemical weapons and to warn that failing to respond "might signal that this is legitimate." Almost immediately, Secretary of State John Kerry was on the phone with Mr. Netanyahu, who then walked back the conclusion by saying he could not "confirm" it -- a statement that Mr. Kerry quickly announced.
At the same time, American and British agents were trying to secure physical samples to test. Majid, a rebel commander who asked to be identified by only his first name, said American intelligence officers in Jordan were provided two sets of hair, soil and urine samples from each of three contested areas near Damascus where rebels have accused the government of using chemical weapons. After positive tests, he said, the officers asked for a third sample, but it could not be delivered along an impassable road.
The British, meanwhile, flew samples first smuggled out to Turkey to a defense facility in England called Porton Down, a chemical weapons research center established during World War I. The British testers were more convinced of the presence of sarin, a nerve agent, than the Americans.
But neither the British nor the Americans could be sure of the "chain of custody," as Mr. Obama calls it. "It is absolutely unclear who used the stuff, in what quantities and to what effect," said a British official. Still, with Congressional hearings in the offing, the White House decided to announce in a letter to Congress on April 25 that chemical weapons had been found.
As Mr. Obama contemplates his response, his advisers are trying to determine why Syria would use such weapons. The Syrian military, while strained, still appears capable of making rational decisions about how and where to deploy forces. It is currently engaged in fierce and ostensibly successful offensives in the Damascus area and in Homs Province. Moreover, two alleged massacres in the past week demonstrated that pro-government militias using knives and guns were capable of inflicting many times the deaths attributed to chemical weapons so far.
Weighing a Response
While Mr. Obama has insisted on more definitive evidence before acting, he has also signaled that he may reverse his decision to reject a plan to provide weapons to the rebels first advanced last winter by David H. Petraeus, then the C.I.A. director, with the support of Hillary Rodham Clinton, then the secretary of state.
Several things have changed since. Britain and France appear likely to begin supplying weapons to the rebels after the expiration of a European Union arms embargo on Syria at the end of May. White House officials say they are also more confident of Gen. Salim Idris, the commander of the rebels' Supreme Military Council, who has rejected ties to groups linked to Al Qaeda. "This is really a bet on Idris," a senior administration official said.
But other administration officials voiced skepticism that funneling weapons to the rebels made any more sense now than it did six months ago. They noted that the rebels are already getting arms from Saudi Arabia, Qatar and other gulf nations, yet forces loyal to Mr. Assad have still made inroads in Homs. While General Idris has made gestures to placate Washington, there is plenty of evidence that the opposition is becoming more, not less, radical over time.
In the meantime, the Syrian government and the rebels continue to trade allegations. On April 25, just hours before the White House sent its letter to Congress announcing the findings on chemical weapons, residents in Daraya, a Damascus suburb, heard explosions. A local doctor and a rebel spokesman said no one was killed but described people suffering from vomiting, excessive saliva, spasms or convulsions, burning eyes and itchy skin.
"There is too much fear, especially for those affected. The next day you walk, you see the dead animals on the street. It was so scary," said the doctor, who called himself Majid. He said he collected urine and hair samples from two victims and consulted two Syrian-American organizations about getting them to the State Department.
Within the administration, the debate over what to do continues.
"The problem here is we react so slowly," said Andrew J. Tabler, a senior fellow at the Washington Institute for Near East Policy. "There have been many well-thought-out plans, but they address a certain context. Then the context changes, we see the situation as rapidly deteriorating, and the recommendations are no longer so finely tuned."
Peter Baker, Mark Landler and David E. Sanger reported from Washington, and Anne Barnard from Beirut, Lebanon. Eric Schmitt contributed reporting from Washington.
This article originally appeared in The New York Times.