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This is MORNING EDITION from NPR News. I'm Renee Montagne.
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The Whitehouse has announced that President Obama's National Security Advisor is resigning and he will be replaced by Susan Rice, the U.S. Ambassador to the United Nations. NPR's Ron Elving is here to tell us more. Ron, some months ago, Ms. Rice was rumored to be nominated Secretary of State - that, of course, did not happen. So why don't you give us a quick fill on the back story.