There's by now a small industry on the thesis that the administration had something to do with 9-11. I've looked at some of it, and have often been asked. There's a weak thesis that is possible though extremely unlikely in my opinion, and a strong thesis that is close to inconceivable. The weak thesis is that they knew about it and didn't try to stop it. The strong thesis is that they were actually involved. The evidence for either thesis is, in my opinion, based on a failure to understand properly what evidence is. Even in controlled scientific experiments one finds all sorts of unexplained phenomena, strange coincidences, loose ends, apparent contradictions, etc. Read the letters in technical science journals and you'll find plenty of samples. In real world situations, chaos is overwhelming, and these will mount to the sky. That aside, they'd have had to be quite mad to try anything like that. It would have had to involve a large number of people, something would be very likely to leak, pretty quickly, they'd all be lined up before firing squads and the Republican Party would be dead forever. That would have happened whether the plan succeeded or not, and success was at best a long shot; it would have been extremely hard to predict what would happen.
One part of the standard story is that they exploited the tragedy for their own purposes, which is certainly true, and was completely predictable; I pointed out in my first interviews a few hours later that every power system in the world would do that, including Washington, as they all did -- one of the easiest predictions. So that shows nothing.
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