JUDY WOODRUFF: The Obama administration said today it believes the Syrian government has used chemical weapons, but it stopped short of saying that the regime had crossed the so-called red line, which would trigger a U.S. response.
Margaret Warner reports.
MARGARET WARNER: The disclosure came initially from Defense Secretary Chuck Hagel, traveling in Abu Dhabi.
DEFENSE SECRETARY CHUCK HAGEL, United States: U.S. intelligence community assesses with some degree of varying confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specifically, the chemical agent sarin.
MARGARET WARNER: At the same time, the White House released letters using exactly the same words from Legislative Affairs Director Miguel Rodriguez to senators Carl Levin and John McCain.
In the letters, Rodriguez added: "We do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime."
But he said the U.S. would need more definitive evidence before deciding to act. "Given the stakes involved," he said, "only credible and corroborated facts that provide us with some degree of certainty will guide our decision-making."
For months, President Obama has warned the Syrian government against using chemical weapons in terms he first used last August.
PRESIDENT BARACK OBAMA: We have communicated in no uncertain terms with every player in the region that that's a red line for us and that there would be enormous consequences if we start seeing movement on the chemical weapons front or the use of chemical weapons. That would -- that would change my calculations.
MARGARET WARNER: Today's disclosure brought calls for a U.S. response from lawmakers in both parties. Republican Sen. John McCain insisted the president must respond quickly.
SEN. JOHN MCCAIN, R-Ariz.: The president of the United States said that if the -- Bashar Assad used chemical weapons, it would be game-changer, that it would cross a red line.
I think it's pretty obvious that red line has been crossed. Now I hope the administration will consider what we have been recommending, and that is to provide a safe area for the opposition to operate.
MARGARET WARNER: McCain urged the administration to impose a no-fly zone in Syria and arm the rebels.
In a statement, Democratic Sen. Dianne Feinstein said: "President Assad may calculate he has nothing more to lose and the likelihood he will further escalate this conflict therefore increases. It is clear that red lines have been crossed and action must be taken to prevent larger-scale use."
Until now, the administration has said it's waiting for the results of an independent U.N. investigation into the allegations. Britain and France said recently they think the Assad regime has used chemical weapons. And Qatar and Israel gave similar assessments last week.
And for more on this, I'm joined by Mark Landler, White House correspondent for The New York Times, and Amy Smithson, a senior fellow at the James Martin Center for Non-Proliferation Studies.
Mark Landler, beginning with you, the White House has up until now refused to say whether it believes the Assad regime has used chemical weapons or they have been used. What's behind the wording of this letter, the rather explicit wording of this letter now?
MARK LANDLER, The New York Times: Well, I think part of it is merely the sequence of event with the British and the French and the Israelis, as you point out, coming out with more and more explicit statements that they believe chemical weapons were used.
There was also a coincidence of a briefing on the Hill when Secretary of State John Kerry was going to brief senators. The White House knew this question would come up. And White House officials say that in the last couple of days, the intelligence community has become much firmer in its assessment that the weapons were used.
So I think there was an extent to which the White House was scrambling to catch up with events and try to get ahead of this by saying something that's now been said by many U.S. allies.
MARGARET WARNER: And in the letter, there was an interesting phrase which Sec. Hagel used too, which he said the intelligence community assessment was offered with -- quote -- "varying degrees of confidence."
What is that supposed to signal?
MARK LANDLER: Well, I think what it signals is that this is not a unanimous, very high level of certainty assessment.
We have been told that really what we are talking about is a range of assessments from medium to high, you know, which is to say that there's a reasonable degree of confidence in the assessment, but not a certainty. And, remember, the administration is presenting this against the history of the Bush administration and the Iraq war, something they alluded to obliquely in the letter to the senators today.
So I think what they're trying to do is show an abundance of caution and not use the intelligence to reach conclusions prematurely, particularly in a case like this where President Obama is on record as being extremely reluctant about being drawn into the conflict.
MARGARET WARNER: Amy Smithson, what is sarin and what is known about the Assad regime's -- whether they have a lot of stockpiles of this?
AMY SMITHSON, Monterey Institute of International Studies: Sarin is a nerve agent, and it is one of several nerve agents that were created during the World War II era.
The Syrian government has long been thought to have an active offensive chemical weapons program that includes not only nerve agents sarin and V.X., but also one that many may remember from the World War I era, mustard gas.
MARGARET WARNER: And when the president's letter -- or, rather, his legislative affairs director letter says that, especially, you know, there are a lot of questions to be answered before a determination could be made to act, what kind of evidence could there be that would actually corroborate, that would constitute credible -- credible evidence?
AMY SMITHSON: If this U.N. investigation team gets on the ground, they're likely to be looking for any number of types of samples, including from any devices that may have been used during these incidents to deliver a chemical agent, from food and water, from clothing, from animals, from humans.
In fact, the announcement today alluded to physiological samples, but they haven't provided clarity as to what those samples might be.
MARGARET WARNER: Mark Landler, do you know what they're referring to when they said that this assessment is based on some physiological samples? MARK LANDLER: Yes, we have an idea that what they are talking about is soil samples, and perhaps other physical samples from people who are injured in the attacks.
So these are things, particularly if it was hair or blood or anything like that that would be very helpful in determining whether there was evidence of a chemical attack.
MARGARET WARNER: Do they say what more they're looking for?
MARK LANDLER: Well, I think the key thing the administration is now looking for is less evidence of the presence of chemicals than evidence of who used them and in what context were they used.
And that goes to the second part of the letter. They need to establish with a certainty that it was the Syrian regime and that the weapons were used deliberately, not accidentally. And that goes to that other important phrase in the letter, that the chain of custody over the weapons wasn't clear. So these are the types of rather difficult conclusions that the administration will now push for, both on its own, working with the Brits and the Israelis, and also through this United Nations investigation.
MARGARET WARNER: But, Amy Smithson, the U.N. investigation which the U.S. has called for is completely stymied, as I understand it. The Assad regime won't let the U.N. inspectors in, at least not so far.
So is there any way to establish a credible chain of custody, as you have described it, and Mark did, that doesn't depend on what might be questionable or unclear sort of agendas of the people who bring it to you, in other words, that are really from independent investigators?
AMY SMITHSON: That would be a challenge.
The investigation that the Syrian government requested was of the incident at Aleppo. But Ban Ki-Moon also wants the inspectors to go to Damascus and Homs. That's why we have a stalemate.
In terms of establishing a chain of custody, what this means is the law enforcement term. If they are videoing where they take the samples, bagging them and tagging them, and very clearly documenting throughout their journey back to a U.S. laboratory or a British laboratory, these samples, preserving them appropriately, then you have credible chain of custody that would stand up even in a court of law.
MARGARET WARNER: Finally, Mark, beginning with you, what would it take or does the administration think it would take to -- if the presence and use of chemical weapons has been established, to actually either neutralize or take control of Assad's assets in that regard?
MARK LANDLER: Well, there are a number of options that the Pentagon has prepared for the president.
The administration today has made it clear that whatever they decide to do, they want to do it in concert with other countries. So it's unlikely to be unilateral. But the types of things that you hear about range from airstrikes on Syrian aircraft and artillery, so they are unable to deliver these weapons, commando raids in to the country to try to secure chemical weapons stockpiles.
So these are the types of things you hear about. What you really don't hear about and what even people like Sen. McCain wouldn't be advising would be any sort of a ground invasion of the country. There's no appetite for having American boots on the ground. So that's almost certain not to be an outcome of this.
MARGARET WARNER: Brief final word from you, Amy Smithson. How challenging is it to secure sites like this, in essentially a hostile country at war?
AMY SMITHSON: Tremendously challenging.
We're probably talking about weapons that are man-portable, if they are loaded already, if the agents are loaded already into rockets. And it could be as large as missiles, because they obviously have missile systems that are capable of delivering this. So it's going to be a big challenge to try to secure it.
But there are some interim steps. And I would hope that somebody is considering getting defensive measures in the hands of Syrian civilians and also the Syrian opposition. We're talking gas masks and clothing and detectors.
MARGARET WARNER: Kind of basics.
AMY SMITHSON: Yes.
MARGARET WARNER: Well, Amy Smithson and Mark Landler, thank you.
MARK LANDLER: Thank you very much.