Obama: Transition Times Vulnerable to Terror Attack

The candidate seeks to explain Sen. Biden's "tested" comment on a Washington, D.C. TV station.

Says any new president will be "severely tested," adding that Bin Laden is still at large and "a lot of times terrorists have tried to deal with transition periods in governments by launching attacks."

Also says his grandmother may not "be around" for the election, and agrees that his impersonator on "Saturday Night Live" isn't quite as talented as Tina Fey.

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