What he is trying to say, as he has said before, that 9/11 was the result of blowback. If America had used Paul’s foreign policy then there never would have been any blowback in the first place.
But if it was the result of blowback then he would have had to travel back in time to 1979 when the Soviet Union invaded Afghanistan and stopped us from helping Osama and friends, or he would have needed to have been president at the time. Either way it’s all hypothetical nonsense using the 9/11 victims for a cheap talking point.
He wasn’t trying to say that he would have noticed a memo that others missed. That’s conjecture and quite presumptuous at that. I’m sure he has perfect vision in hindsight.