The Iraqis are equally to blame for not providing outside security and allowing these thugs into the Green Zone. These imbeciles in the streets around the embassy could easily be dispersed with one low flying Apache gunship.
The Green Zone isn’t as locked up as it used to be. It is a big area, and there are a bunch of tall apartment buildings just across the street from the embassy, inside the old Green Zone, full of civilians.
The lower ranking guys are not going to confront one of these organized groups, until directly ordered by their superiors, so there will be a natural lag in response.
Things got elevated quickly, and Iraqi forces were dispatched. The Iraqi Interior Minister himself (Head of internal security), arrived on scene, and went into the US Embassy. Any Iraqi would expect to be killed if he caused injury to that guy.
At least one Apache was on the scene, came in for a low hover, and deployed flares right over the crowd (some threat may have triggered the release /s).
If this was a rehearsal/probe for a future assault, the next time they will encounter a different situation. A hundred more Marines have already arrived at the embassy, and other reinforcements are on the way.