Blast(literally) from the distant past:
Before 9/11 America was a wide open society just waiting to be attacked by Islamic wackos.
True! One simple element that was discussed many times before 9/11 but no actions were taken, was the flimsy door between the commercial airline pilot & the passengers. All four doors in each of the four 911 airliners were broken through by the terrorists easily. An impenetrable door would have nixed the terrorist plans.
Even one of Tom Clancy's books, Executive Order talked about someone with a 400+ ton airliner (with 250 TONS of fuel) taking out the Congress in a deliberate kamakaze explosive attack. The military knew the risk & didn't take appropriate action.