Surprisingly, the terror threat posed by al Qaeda and other terror groups did not top this year's version of the Worldwide Threat Assessment prepared by the US Director of National Intelligence (DNI).

"Senior personnel losses in 2012, amplifying losses and setbacks since 2008, have degraded core al Qaeda to a point that the group is probably unable to carry out complex, large-scale attacks in the West," said Clapper. Those losses have come from the CIA's controversial drone strike program in Pakistan's tribal areas where al Qaeda leaders are believed to continue to operate.

 While "core al Qaeda" has been weakened, its affiliate in Yemen, al Qaeda in the Arabian Peninsula (AQAP), has pursued attacks on U.S. interests like the unsuccessful underwear bomber attack in 2009. A similar attack was thwarted last year around the time of the one year anniversary of bin Laden's death.

The threat posed by AQAP led to an expansion of the CIA's drone programme into Yemen targeting the group's leaders including American born Islamic cleric Anwar al Awlaki.

Bruce Hoffman, a counterterrorism expert at Georgetown University, says bin Laden's death in May 2011 was regarded "as a decisive corner having been turned in the war on terror" and agrees that it hastened the terror network's decline. However, he is concerned by what he calls the "rise in al Qaedism" whose message of Islamic militancy targeting the U.S. has resonated in places like northern Africa where last September's deadly attack on the U.S. consulate in Benghazi was believed to have been carried out by al Qaeda supporters.

State of Terror Two Years After Osama bin Laden's Death

"We see the threat of its ideology to places where hitherto it really was not terribly strong or salient and we see almost a revival of its brand," says Hoffman. He adds that Islamic terrorists continue to cite al Qaeda as an influence and "aspire to emulate al Qaeda's ideology" of a violent struggle against the United States. "I think the challenge of al Qaeda remains," says Hoffman. "We may want to wish it away, and we may want to believe that killing bin Laden killed off the brand, or killed off the ideology, but we don't see any evidence of that." Brian Jenkins, with the Rand Corporation, agrees that bin Laden's death had "an immediate impact" on the group's morale and believes it became even more decentralized and dependent on its allies and affiliates since his death which could erode the group's ideological focus of a violent struggle against the United States.

"One of the things bin Laden did by his very existence was maintain a unanimity of focus, a degree of unity, a single-minded focus on its ideology," says Jenkins. While bin Laden's successor, Ayman al Zawahiri, has struggled to maintain that ideological focus Jenkins believes it could continue to erode and al Qaeda could fragment into many localized movements.

Jenkins is concerned that an "opportunistic" al Qaeda could be resurgent in Syria and Afghanistan. In Syria, Islamic extremists are playing a growing role in the fight to topple President Bashar al Assad leading to concerns about what a post-Assad Syria might look like. In Afghanistan, Jenkins is concerned that al Qaeda could once again find a safe haven in that country should the Taliban expand its control after U.S. combat forces pull out by the end of 2014.

"We have to presume this sort of thing will go on," said Jenkins. "All of these are opportunities for al Qaeda. It's not the same al Qaeda it was on Sept. 11. It's very different and it's still there, and I for one wouldn't exaggerate its death, but I'm not writing its epitaph right now."

Another possible indicator of al Qaeda's diminishing role is the decrease in the number of the CIA's drone strokes in Pakistan this year. Hoffman speculates the decrease could be the result of fewer al Qaeda targets or because "we don't have the intelligence to identify emergent al Qaeda leaders and single them out." He also thinks it might be possible that al Qaeda has gone underground in Pakistan's large cities.

The full testimony of DNI James Clapper to the US Senate, can be accessed at http://www.intelligence.senate.gov/130312/clapper.pdf