My guess: it was Susan Rice who prevailed upon Obama not to allow the rescue mission to move forward.
The logic may have been that it would be easier to explain American deaths in Libya than it would have been to explain what they were doing there in the first place. Dead men tell no tales.
Very many reports say that they were there to facilitate illegal, undocumented, arms sales to Syrian 'so called' rebels. Which were really Al Quada and ISIS fighters. It is important to remember that Obama, as a huge fan of the Muslim Brotherhood, envisioned his own kind of 'Caliphate'. What Obama wanted, and he called it the "Arab Spring", was MB control of the entire Mediterranean crescent.
Obama had already installed the MB as the government of Egypt. He had Libya destabilized and ready for an MB take over with an utterly and absolutely 'illegal' war. And that's what he had in mind for 'new Syria' (and Lebanon with them of course). Eventually, had he been successful, Obama would have moved his MB forces into Syria, Tunisia, Jordan, Algeria, Morocco, Iraq, all with U.S. force support. And who knows where he would have gone after that. They certainly would have attacked Israel eventually, which Obama and his MB crew viewed as the 'cherry on top' of it all. Obama's hatred for Israel is well known. He would have supported an attack on Israel with glee but it never got that far.
It is interesting that the Muslims themselves stopped Obama. America, the U.N., and Europe were docile little lambs, either tacitly supporting what Obama was doing, or abstaining. But the Muslims fought Obama's plan, because they have no patience for the Muslim Brotherhood. Egypt overthrew Obama's MB installed government. Al Queda took over Libya, leaving no room for the MB to move in. And Obama's illegal operations in Syria were exposed and curtailed. That was the end of Obama's Arab Spring. But it was the Muslims who stopped him. Not any of the Western powers. Even to this day, Obama is reviled in Egypt and in most of the M.E.
Benghazi was the beginning of the end of Obama's plans for domination of the Middle East. It brought the whole scheme to light in a way he and his administration never expected.
