At a White House news conference, Obama said the United States has worked to strengthen the opposition and worked with allies to help Bashar Assad to be forced out of office.
Obama said use of chemical weapons is a "game changer" for not just the United States but the international community as well. He said though there's evidence chemical weapons were used, there remain questions about who was responsible.
He said he will not "rush to judgment."
Notable deaths of 2014 [PHOTOS]