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But as NPR's Tom Gjelten reports, six weeks have passed since bin Laden was killed, and some experts wonder if the delay in naming a new leader means that Zawahiri faced some competition.
TOM GJELTEN: As the official number two, Zawahiri was set to take over Al-Qaida after bin Laden's death, but his selection had to be ratified by the group's leadership council. Zawahiri may even have felt the need to campaign for the position.
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AYMAN AL: (Foreign language spoken)
GJELTEN: In any case, Zawahiri does now have al-Qaida's official backing. Defense Secretary Robert Gates made that point today at the Pentagon.
ROBERT GATES: I think he's got some challenges, but I think it's a reminder that they are still out there, and we still need to keep after them.
GJELTEN: One question is whether Zawahiri will be a different kind of al-Qaida leader than bin Laden was. Terrorism expert Bruce Riedel of the Brookings Institution notes that he's more of an ideologue - writing books and making lots of public statements - whereas bin Laden kept a fairly low profile.
BRUCE RIEDEL: Zawahiri is probably someone we're going to hear from more. But while he is a thinker, it's a mistake to assume he's not also a doer. This is a man who's been involved in a lot of nasty terrorist planning. So he's willing to mix it up and get right in there. And I think it would be a mistake to underestimate this guy.
GJELTEN: Tom Gjelten, NPR News, Washington. Transcript provided by NPR, Copyright NPR.