I meant to respond to this earlier this week, but I think the notion that al-Qaeda is on the verge of defeat would best be taken with more than a grain of salt. As Daveed Gartenstein-Ross points out, we've heard this before -- government officials have been periodically writing al-Qaeda's obituary since 2003:
President Bush claimed in September 2003 that al-Qaeda was on the ropes. As Time reported, he told the nation that up to two-thirds of the group’s known leadership was captured or killed; the same Time story said that “its training camps in Afghanistan have been destroyed and the relentless worldwide campaign [against it] has denied it new sanctuaries.” In April 2006, the consensus of the intelligence community was that al-Qaeda had in fact been defeated as an organization. The National Intelligence Estimate released that month said that “the global jihadist movement is decentralized, lacks a coherent strategy, and is becoming more diffuse.” The following month, President Bush shared this cheery assessment, saying, “Absolutely, we’re winning. Al-Qaeda is on the run.”
The current optimism seems to be driven by the death of Osama bin Laden. I think it's a bit early to know how his death will affect al-Qaeda, but as I've noted before, the history of terrorist organizations is that they recover fairly quickly from loss of leadership as long as the underlying issues driving their existence remain.
On the other hand, this sounds more true than not:
“But if you mean that we have rendered them largely incapable of catastrophic attacks against the homeland, then I think Panetta is exactly right,” the official said, speaking on the condition of anonymity to discuss sensitive intelligence. “We are within reach of rendering them to that point.”
That's good news, although it's still far from al-Qaeda being on "the brink of defeat."