The Big Question: What does US intelligence consist of and does the system need overhauling?

Why are we asking this now?

On Christmas Day, the Nigerian student Umar Farouk Abdulmutallab came within an ace of detonating an explosive device hidden in his underclothes that would have probably caused the destruction of Northwest Airlines flight 253 as it prepared to land in Detroit, killing hundreds of people.

It later emerged that US intelligence had several clues that such an attack might happen; as one expert put it, "You're never going to have more warning of an attack than this one." President Obama was reportedly even blunter at a meeting of top national security and intelligence officials at the White House on Tuesday, describing what happened (or rather didn't happen) as "a screw-up that could have been disastrous".

Isn't all this terribly familiar?

Indeed it is. In 2001, US intelligence and law enforcement had pointers that a terrorist attack was being planned on targets within the US. Yet the various agencies failed to pool information (ranging from suspected terrorists applying for visas to young Arab men taking lessons on piloting commercial airliners) and on 11 September the unimaginable happened.

The authorities vowed, never again. But the mistakes of 12/25 bore an uncanny resemblance to those of 9/11. Once again information was not properly analysed and circulated.

Who was involved?

This is a large part of the problem. The US intelligence community consists of no less than 16 separate agencies – the CIA of course, as well as 15 others spread across six cabinet departments, including no less than eight under the aegis of the Pentagon alone. They employ an estimated 100,000 people and share a combined budget said to be close to $50bn (£31bn).

For connoisseurs of alphabet soup, these agencies are (in roughly descending order of importance): the CIA, the FBI, the NSA, the DIA, the INR, the NRO, the NGA, the AFISRA, MI, the ONI, the MCIA, the OICI, the I&A, CGI, the DEA, and the TFI. Got it?

Historically moreover, relations between them have not always been smooth, while the sheer number of agencies means there will invariably be differences of opinion that get in the way of swift, concerted action.

How do the agencies get on?

Over the years, the most damaging tensions have been between the two best-known agencies, the CIA and the FBI, who between them do the same job as MI6, MI5 and Special Branch in Britain. The inability of the CIA and the FBI to work together properly was especially glaring in the run-up to 9/11. It also contributed to the long failure to expose the CIA mole Aldrich Ames, finally unearthed in 1994 after a devastating nine-year career as a spy for Moscow.

Separate differences emerged in the run-up to the Iraq War, with the intelligence arms of the State Department and the Energy Department (it runs the Office of Intelligence and Counter-intelligence, or OICI) notably more sceptical than the Pentagon and the CIA over Saddam Hussein's nuclear programme.

Wasn't this sorted by post-9/11 reforms?

The operative word is "supposedly". After 2001, everyone agreed it was time to streamline the country's intelligence structure. So, in the best bureaucratic tradition, two more agencies were set up. One was the Office of the Director of National Intelligence, headed by a DNI to whom the 16 existing agencies would report.

Among other things, this meant the end of the CIA's traditional position of primus inter pares in the intelligence community – a demotion that predictably did not go down too well in some quarters of the CIA. This change was supposed to have the various agencies singing off the same hymn sheet.

Simultaneously, a new National Counterterrorism Center (NCTC) was created by President Bush in 2003, to act as clearing house for information on terrorists and potential threats.

Why wasn't the US able to catch Abdulmutallab?

The old faults had not been eradicated. In this case, the NSA, or National Security Agency – the huge global eavesdropping agency that is the US equivalent of the Cheltenham-based GCHQ in Britain – reportedly picked up "chatter" within Yemen before 12/25 about a "Nigerian" who had been trained for an attack on an American commercial jetliner. Meanwhile, Mr Abdulmutallab's father actually warned the CIA and other officials at the US embassy in Nigeria that his son had alarming extremist views and contacts.

But these two "dots" (more like footballs, some would say) were not connected, and the son's multiple-entry visa to the US was not revoked. Once again, the NSA, the State Department and the CIA seem not to have shared what they knew. As President Obama put it, "intelligence was not fully analysed or fully leveraged". The NCTC is believed to have complained that it was kept in the dark by the NSA and CIA about aspects of the case.

Was the international co-operation also lacking?

It has been suggested that Britain, where Mr Abdulmutallab studied between 2005 and 2008, failed to pass on to the US information gathered by MI5 about his extremist links. But this is hotly denied by the British authorities.

Similarly there have been complaints the Dutch did not look closely enough at Mr Abdulmutallab, who boarded the Detroit-bound plane in Amsterdam.

But the main responsibility must lie with the US, who despite the multiple clues, did not place him on a list of 14,000 individuals subject to special airport screening. Instead he featured merely on a list of 550,000 people suspected of links to terrorism, too unwieldy to be of much use.

Will the Obama scolding produce results?

Everyone says so. "The intelligence community received the President's message today," declared Dennis Blair, the DNI. "We got it, and we are moving forward to meet the new challenges." But similar promises were made after 9/11, and after the intelligence re-organisation that set up the ODNI and NCTC.

The problem is not a lack of information, but a failure to make use of the prodigious quantities of information amassed by the various agencies, in particular the NSA. We come back to an eternal truth of counter-terrorism and counter-espionage in general. Technology will only get you so far. What matter are the human beings who at some point must process what technology has provided.

So no system can be entirely fireproof?

That's right. As Mr Obama this week observed, intelligence by its very nature is imperfect. A balance must also be struck between security precautions and personal liberties. Had Mr Abdulmutallab (and every other passenger on Flight 253) for instance been shackled to their seats, the attempted suicide-bombing would have been impossible.

That of course would have been intolerable. It would in this case also have been unnecessary, had the US intelligence community functioned as it is supposed to function.

Will the system now work more efficiently?

Yes...

* This time, the lesson surely has been learned that co-operation is essential

* Despite this failure, US intelligence agencies are co-operating better than before 9/11

* Mr Obama's own political survival is reason enough for those charged with protecting the US to get their act together

No...

* Terrorists will always find a way to be one jump ahead, no matter how much scrutiny they are under

* Without a really strong Director of National Intelligence, bureaucratic reform cannot do the trick

* Deep down, the United States is just not very good at spying and related activities