8/30: 60k evacuate ahead of dam's "imminent failure"; Mitt Romney's big night

      |A dam in southern Mississippi is at risk of "imminent failure" from flooding brought on by Hurricane Isaac. Byron Pitts reports from downstream in Kentwood, La., where the entire town is being evacuated; And, Mitt Romney will accept the GOP presidential nomination at the Republican National Convention and deliver a speech designed to reintroduce him to the nation. Norah O'Donnell reports on what to expect on Romney's big night.

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