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Florida school shooting repeats all-too-familiar pattern, Lester Holt says

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The shooting at Marjory Stoneman Douglas High School in Florida that took 17 lives is only the latest milepost on a road of anguish that includes Columbine, Virginia Tech and Sandy Hook. NBC Nightly News anchor Lester Holt reflects on what has become a heartbreaking – but all too familiar – American story.