We know that the post communicated to the Department that they could not depend on the host government for protection. That alone should have mandated the closure of the post.
The host government is responsible for external security outside the embassy wall. The marines usually have responsibility for the inside. Most embassies have 9-11 marines. After 9-11 I think Pakistan increased to 22. So there is some responsibility for marines to provide protection.
Don’t recall marines at Benghazi, but I welcome information to the contrary.