Yes, there was risk of hijacking. But up until 9/11, the hijackings never resulted in ramming the planes into buildings. Add in the fact that we hadn't had a domestic hijacking in about 30 years? The threat was always deemed to come from outside in. 9/11 changed that.
So, the military was just inept. That alone is frightening. It is the one thing that has always perplexed me, how our highly trained military was ineffective and no one thought anything of it.
The whole investigation into what went wrong that day was inept.