Debunking the "NSA Mass Surveillance Could Have Stopped 9/11" Myth

It's something that we're hearing a lot, both from NSA Director General Keith Alexander and others: the NSA's mass surveillance programs could have stopped 9/11. It's not true, and recently two people have published good essays debunking this claim.
The first is from Lawrence Wright, who wrote the best book (The Looming Tower) on the lead-up to 9/11:

Judge Pauley cites the 9/11 Commission Report for his statement that telephone metadata "might have permitted the N.S.A. to notify the [F.B.I.] of the fact that al-Mihdhar was calling the Yemeni safe house from inside the United States." What the report actually says is that the C.I.A. and the N.S.A. already knew that Al Qaeda was in America, based on the N.S.A.’s monitoring of the Hada phone. If they had told the F.B.I., the agents would have established a link to the embassy-bombings case, which "would have made them very interested in learning more about Mihdhar." Instead, "the agents who found the source were being kept from obtaining the fruits of their work." The N.S.A. failed to understand the significance of the calls between the U.S. and Yemen. The C.I.A. had access to the intelligence, and knew that Al Qaeda was in the U.S. almost two years before 9/11. An investigation by the C.I.A.’s inspector general found that up to sixty people in the agency knew that Al Qaeda operatives were in America. The inspector general said that those who refused to coöperate with the F.B.I. should be held accountable. Instead, they were promoted.

The second is by Peter Bergen, another 9/11 scholar:

But is it really the case that the U.S. intelligence community didn't have the dots in the lead up to 9/11? Hardly. In fact, the intelligence community provided repeated strategic warning in the summer of 9/11 that al Qaeda was planning a large-scale attacks on American interests.
[...]
All of these serious terrorism cases argue not for the gathering of ever vaster troves of information but simply for a better understanding of the information the government has already collected and that are derived from conventional law enforcement and intelligence methods.