Defense Secretary Robert Gates talks with troops during a visit April 7 at Camp Victory in Baghdad. Chip Somodevilla/Getty Images hide caption

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Residents survey the destruction after a tornado hit Pratt City, Ala., on April 27. Short-term forecasting of twisters like the ones that swept the South this week has grown increasingly accurate, but long-term forecasting remains highly unreliable. Butch Dill/AP hide caption

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U.S. Rep. Paul Ryan, R-Wis., right, hears from a constituent during a "listening session" Tuesday at Gateway Technical College in Kenosha, Wis. Ryan's plan to fundamentally restructure Medicare and cut social safety net programs has proved to be a tough sell to many Republican voters the last few weeks. Jeffrey Phelps/AP hide caption

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