I believe this is when he gave the order not to send them air cover. The White House uploaded this picture today (taken on 9/11/12).

(Sept. 11, 2012)  – “Denis McDonough, Deputy National Security Advisor, left, updates the President and Vice President on the situation in the Middle East and North Africa. National Security Advisor Tom Donilon and Chief of Staff Jack Lew are at right.” (Official White House Photo by Pete Souza)