No one knows the future. They had sent an available force that was in country. That force was delayed. The former Seals had driven off several attacks and had survived for several hours. They may have thought that they would make it without bringing assets from out of country.
It could be simple incompetence aggravated by political machinations and a willingness to coverup and prevaricate, believeing that the MSM can and will cover for you.
The thing that leads me to believe it was not incompetence or just wanting to not have a Jimmy Carter moment right before the election is the refusals in advance to allow more security for Stevens.
And the fact that the White House knew anything about this video that had hardly any views and was created/uploaded by a terrorist cousin of Walid Shoebat who has connections with the Muslim Brotherhood (that planned the 9-11 shenanigans in Egypt), as well as linking to Obama stuff.
Those things really look like advance preparations for this event, not just incompetence. Obama vetoed his Secretary of State to make sure that Stevens was not protected, after a 40-foot hole had been blown in the wall of the consulate. That’s not incompetence. Obama can say he didn’t know about added requests for security, but if Hillary requested additional security and it got vetoed, my understanding is that there is only one person who could have done it. Obama HAD to know, and he personally made sure that Stevens was unprotected.