What does the President need to know?
The CIA has released 2,500 top secret briefings from the 1960s given to Presidents John F Kennedy and Lyndon B Johnson. The President's Daily Brief - or "PDB" - is the US intelligence agencies' best assessment of global threats, delivered in person every morning.
The briefings highlight an almost impossible dilemma, one still faced today by every director of National Intelligence: what should, and should not, be included?
Former US director of National Intelligence John Negroponte delivered the PDB to President George W Bush. He spoke to the BBC World Service Inquiry programme about what the president needs to know:
"The President's Daily Brief represents the best effort of the intelligence community to present the best possible analysis of current events that are of policy interest to the White House and the United States government.
A typical brief will have six or seven articles, usually not exceeding one page, sometimes just a paragraph. And then one or two longer 'deep dive' pieces.
There's a presidential daily briefing staff that works around the clock. The bulk of articles are prepared by CIA analysts.
The analysts draft some briefs the previous evening, then spend until about two or three in the morning polishing the articles, and then complete the PDB sometime around four or five o'clock in the morning.
I had a small classified fax machine in the basement of my house with a guard standing over it, and I would usually read the first draft before bed. I would wake about five, listen to the radio, read the newspapers and then go into the office.
I would meet the analyst who was going to brief the president at 6:30, and we'd go over the product. Very rarely we might decide to omit a particular article, not because we're holding something back, but because we felt the product could improve, might not be ready for prime time.
And then a few minutes before 8:00 we would go to the outer office of the president until he was ready. He took that briefing every day of the week, Monday through Friday, and Saturdays as well. He was very disciplined about it, and he was what the intelligence community would call 'an excellent customer'.
He was interested and anything but passive. He'd interrupt and say 'I don't really believe that, let's talk about this' or 'would you please look into this part more?' or 'could you also answer this question?'
He had a dialectic style where he liked to come to a better understanding of what was being presented to him through discussion and debate.
"These meetings usually went for 30 minutes, unless he got terribly interested in something and we might spill over. With him he had the vice president, the National Security Advisor, and his chief of staff.
Our mission was to present him with the best possible assessments of the various situations of concern, whether it was the situation in Iraq, or the leadership competition in Iran: difficult subjects that were very germane to the policies that he was either carrying out or developing, based on clandestinely obtained information that might not be otherwise be available.
How do you decide what goes in? What do you decide to put in the BBC headlines? How does the editor of the New York Times decide what stories to give priority to? It's a sifting process, and if you're the president, you have to let people below you prioritise what they think is important.
And equally important is what then do you choose to really analyse? Because it's one thing to have the headline, but then to make sense out of what's going on you've got to go beyond that and try to understand the underlying factors and the root causes.
I would present the annual intelligence assessment in its unclassified version to the Congress, and some congressman would pipe up and say 'I could have read this in the New York Times.'
But that's our best assessment of what is really happening. You might have been able to read it in a newspaper but it carries the weight, the imprimatur of the intelligence community, and a lot of sophisticated and intense analytic work.
Every week the Director of National Intelligence would bring together the major agencies - the CIA, the Defence Intelligence Agency, the National Geospatial Agency, the National Reconnaissance Office, and the FBI - to go over issues of common concern, talk about different analytic and collection issues.
'Sort the signals from the noise'
But rarely is intelligence a panacea. It is information based on the best possible sources that helps you narrow the range of uncertainty, that improves the confidence with which leaders can make decisions.
Sometimes you get one of those silver bullets, like we got the phone number of Abu Musab al-Zarqawi [the head of al-Qaeda in Iraq], and if you have that then, of course, you can work with the National Security Agency, or GCHQ, to track his movements,
I remember when we intercepted an absolutely fascinating letter that Ayman al-Zawahiri (now head of al-Qaeda, then Bin Laden's number two) had sent to Abu Musab al-Zarqawi. We actually intercepted it before Zarqawi read it.
It was a long discourse on Zarqawi's tactics, asking him to tone them down. Rather amusingly at the end Zawahiri said 'By the way, could you please send us €100,000?'. So the branch office, al-Qaeda in Iraq, was richer than headquarters, and headquarters was asking him for money.
Afterwards we had quite a debate in the White House about whether we should release that letter publicly. The president favoured releasing it. I was a little bit reluctant but we eventually did, and it makes for very good reading.
But intelligence failures are real. Hindsight is 20/20 vision and you can always connect the dots after the fact. You look back and you can identify the bits of information that you missed, and that you failed to connect to some event that subsequently occurred.
But let's be honest, there's a lot of noise. Like Pearl Harbor; we knew something was going to happen, we didn't know exactly where and what.
You have to sort the signals from the noise, you have to find which are the signals that really matter. And that's a matter of skill on the one hand; it's a matter of luck on the other.
The key point about 9/11 was surprise.
The same thing with the Cuban missile crisis, when we discovered the Soviets were going to send intercontinental missiles to Cuba.
Believe it or not, two months before, the intelligence community had published an analysis saying the Soviets would never even dream of sending intercontinental ballistic missiles to Cuba.
I looked at the PDBs that were released from the end of the Johnson Administration, and here's the problem I see.
The redaction and vetting process is so rigid, and so careful, that if these articles had any real meat to them they get excised from the unclassified versions. There was one article, it was article number three on a particular day, and the subject was 'Canada', and then the rest was just a blank page.
What are you going to do with that? Unless some guy like Mr Snowden gets hold of them and leaks them, in terms of deliberate declassification, I think that the intelligence community, especially the CIA, is going to always err on the side of caution when it comes to declassification.
So you're not going to learn a lot from them."