And now, only one senior al Qaeda leader left

Editor's note: Peter Bergen, CNN national security analyst, is the author of "Manhunt: The Ten-Year Search for bin Laden, From 9/11 to Abbottabad."

Washington (CNN) -- The news that Abu Yahya al-Libi, the No.2 leader of al Qaeda, is now confirmed to have been killed in a CIA drone strike in Pakistan's tribal region along the border with Afghanistan further underlines that the terrorist group that launched the 9/11 attacks is now more or less out of business.

Under President Barack Obama, CIA drone strikes have killed 15 of the most important players in al Qaeda, according to a count maintained by the New America Foundation (a nonpartisan think tank where I am a director).

Similarly, President George W. Bush also authorized drone strikes that killed 16 important al Qaeda operatives in Pakistan while he was in office.

Peter Bergen during coverage of CNN's Anderson Cooper 360 on location in Afghanistan

As a result, according to senior U.S. counterterrorism officials, there now remains only one leader of any consequence in al Qaeda and that is Ayman al-Zawahiri, the tetchy Egyptian surgeon who became the head of the group following the death of its founder, Osama bin Laden, in a U.S. Navy SEAL raid in Pakistan in May 2011.

Zawahiri, presumably, is keenly aware of the fate of so many of his longtime colleagues in al Qaeda. He will be expending considerable energy not to end up on the business end of a missile fired by a CIA drone if he, too, is hiding in the Pakistani tribal regions where the drone strikes have been concentrated.

Meanwhile, Zawahiri faces an almost impossible task to follow through on al Qaeda's main mission: attacking the United States, or failing that, one of its close allies.

Al Qaeda hasn't conducted a successful attack in the West since the bombings on London's transportation system on July 7, 2005, and of course, the group hasn't succeeded in attacking the United States for more than a decade.

Al Qaeda No. 2 killed in drone strike

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There are, however, al Qaeda's regional affiliates still to contend with. The most virulent of those is the Yemen-based Al Qaeda in the Arabian Peninsula. It was AQAP that tried to bring down Northwest Flight 253 over Detroit on Christmas Day 2009 using a Nigerian recruit who had secreted a hard-to-detect bomb in his underwear, and it was AQAP that smuggled bombs in printer cartridges onto cargo planes bound for the U.S. in October 2010.

Last month came news that a spy had penetrated AQAP and had retrieved a new generation of underwear bomb that the group's bomb maker had apparently recently designed to bring down a commercial jet.

But all of AQAP's plots to bring down planes have had one thing in common: They failed.

Some might say that that while al Qaeda the organization may be basically dead, its ideology continues to thrive and to inspire "lone wolves" to attack the United States.

In fact, lone wolves inspired by jihadist ideology have managed to kill a total of 17 Americans in the United States since 9/11, according to a tally maintained by the New America Foundation.

Meanwhile, 54 Americans are reported to be killed every year by lightning, according to the National Weather Service. In other words, to the average American, lightning is about 30 times more deadly than jihadist terrorism.

Few Americans harbor irrational fears about being killed by a lightning bolt. Abu Yahya al-Libi's death on Monday should remind them that fear of al Qaeda in its present state is even more irrational.

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