That’s the part you’ve heard about: failure to protect the personnel at the embassy.
But then Hersh breaks the deeper story wide open:
A highly classified annex to the report, not made public, described a secret agreement reached in early 2012 between the Obama and Erdoğan administrations. It pertained to the rat line. By the terms of the agreement, funding came from Turkey, as well as Saudi Arabia and Qatar; the CIA, with the support of MI6, was responsible for getting arms from Gaddafi’s arsenals into Syria. A number of front companies were set up in Libya, some under the cover of Australian entities.