On Thursday, the White House informed Congress of the likely use of chemical weapons in Syria, saying the intelligence community has come to the conclusion with "varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin."
US Defense Secretary Chuck Hagel also confirmed the news, saying, "The decision to make this conclusion was reached in the last 24 hours."
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Since the uprising in Syria began in April 2011, the Obama administration has condemned Syrian President Bashar al-Assad's regime, called on Assad to step down and drawn red lines for US involvement.
To put the news in context, here's a timeline of significant previous US statements on Syria:
April 8, 2011: In response to the violent crackdown of the uprising in Syria (which began March 15), Obama said, "I strongly condemn the abhorrent violence committed against peaceful protesters by the Syrian government today and over the past few weeks. I also condemn any use of violence by protesters."
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He added, "I call upon the Syrian authorities to refrain from any further violence against peaceful protestors. Furthermore, the arbitrary arrests, detention, and torture of prisoners that has been reported must end now, and the free flow of information must be permitted so that there can be independent verification of events on the ground."
July 12, 2011: Obama sharply rebuked Assad, saying he had "lost legitimacy" during an interview with CBS News. At that point, his statement on action was still vague, "That's why we've been working at an international level to make sure that we keep the pressure up, to see if we can bring some real change in Syria."
White House spokesman Jay Carney echoed Obama's words, saying, "President Assad is not indispensable." He continued, "We had called on him to lead this transition. He clearly has not, and he has lost legitimacy by refusing to lead the transition."
August 18, 2011: For the first time, Obama openly called on Assad to step down. He said, "For the sake of the Syrian people, the time has come for President Assad to step aside."
On the United States' role in the struggle, Obama said, "The United States cannot and will not impose this transition upon Syria. It is up to the Syrian people to choose their own leaders, and we have heard their strong desire that there not be foreign intervention in their movement. What the United States will support is an effort to bring about a Syria that is democratic, just, and inclusive for all Syrians."
The statement was followed by deep sanctions imposed on the Syrian government and members of Assad's regime.
June 22, 2012: Then Defense Secretary Leon Panetta defended the Obama administration's decision not to arm the Syrian rebels, saying it would push the country further into civil war.
"We made a decision not to provide lethal assistance at this point. I know others have made their own decisions," he said, referring to reports that some Gulf states has decided to arm the rebels. "If we don't get this done in a responsible way, there's a real danger that the situation there could deteriorate into a terrible civil war."
July 23, 2012: Obama warned Assad not to make the "tragic mistake" of using chemical weapons. While talking to US veterans, Obama said, "Given the regime's stockpile of chemical weapons, we will continue to make it clear to Assad and those around him that the world is watching."
"They will be held accountable by the international community and the United States should they make the tragic mistake of using those weapons," he continued.
The statement came in response to Syrian foreign ministry spokesman Jihad Makdissi warning that Syria might use chemical weapons if attacked by outsiders.
"Syria will not use any chemical or other unconventional weapons against its civilians, and will only use them in case of external aggression," said Makdissi.
August 20, 2012: Obama for the first time used the term "red line" when referring to chemical weapons use in Syria. He said, "We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people."
"We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus. That would change my equation," he said.
"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."
December 3, 2013: Obama once again talked of red lines, saying, "I want to make it absolutely clear to Assad and those under his command. The world is watching. The use of chemical weapons is and would be totally unacceptable. And if you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable."
March 20, 2013: On his highly symbolic trip to Israel, Obama called the use of chemical weapons a "game changer." He said he was "deeply skeptical" of claims by Assad's regime that rebels were behind the use of chemical weapons.
"We know the Syrian government has the capacity to carry out chemical weapon attacks," he said, during a joint press conference with Israeli Prime Minister Benjamin Netanyahu.
"We know that there are those are in the Syrian government who have expressed a willingness to use chemical weapons if necessary to protect themselves. I am deeply skeptical of any claim that in fact it was the opposition that used chemical weapons. Everybody who knows the facts of the chemical weapons stockpiles inside of Syria as well as the Syrian government capabilities, I think, would question those claims."