I don't think it's too out of line to say there's fault here that's being at best ignored, and at worst actively covered up.
Over 20 warnings that year, (sources vary, up to 28 or so, and that's reported warnings), threats and warnings going back to the nineties. Now I'm sure there were shedloads of other threats and warnings too... Now I'm sure it's a lot of people deciding which threats are credible/important enough to look into, but if the reported warnings are correct, as of August 2001 the security agencies of the western world knew that Al Qaeda had the intention of attacking US landmarks, had agents on US soil, maybe learning to pilot planes.
That, to me, sounds credible, and the combination of Planes plus Landmarks can help work it out. I'd like to think (Admittedly, hindsight is always 20/20) that if I had been bought these pieces of info, I could have come up with a list of possible targets, and the Twin Towers would be in my top 5.
Then, for Bush et al, to do their official speeches and press conferences and to look into a camera at millions and say, with a straight face, "We had no way of knowing", "We could not conceive of this"... Negligence. Negligence leading to thousands of dead people. Negligence that was lied about afterwards. Negligence with no consequences. It's not hard to understand why some people think the government had a hand in it.
I do feel you might rather enjoy the mini series The Path to 911, or perhaps PBS' The Man Who Knew. It will outline Bodine's role, who in my opinion was the unlocked gate that let all this happen. I think there were many other people covering their backsides too, which I am not sure is nefarious, but perhaps more along the lines of self preservation. Bodine stopped the one guy who knew the attack was going to happen, and who knew who would mastermind it. He was a playboy with a wife and a Girlfriend, and Ms Bodine took quite some offence to his footloose lifestyle. She teamed up with a man called PIkard and together they stopped John ONeil from investigating the operation in it's early stages. He ended up head of security at the WTC and perished in the attacks.
As such, it is hard to say who really knew what. Bodine's roadblock reached all the way to Yemen. But if one person could have stopped this from happening, it was her.
You are right, they could have conceived of this, that is no doubt an exaggeration, but not one I would hang someone on. Wether Oneils information ever reached the right places is more than dubious, but had it been taken seriously, I feel it is very possible that 911 would never have happened. The Bojinka Plot was rather similar in design. That alone says they should have suspected it was possible, however, that does not mean they knew it would happen either.
We know mistakes were made, we even know who dropped the ball. I am not sure why people like Bodine were not immediately dishonorably dismissed, but I do not feel that indicates that she has some powerful personal influences. The kid gloves used to handle her are suspicious, and I can see why people would ask questions, but I do not see that it would absolve the very fact that the killers on 911 were heralded by their religion in many parts of the world. It's no mystery who did it, a bigger one is why so many CT'ers want to see the people who we know are responsible walk away. From what I can tell, it's a personal thing.
I am pretty glad Bodine is not looking after my country.