Sen. Tom Harkin Sen. Tom Harkin

Democratic presidential candidate Hillary Clinton speaks at the Iowa Democratic Wing Ding at the Surf Ballroom on Friday. Appearing at the Iowa State Fair on Saturday, she said the controversy over her emails was the "usual" politics. Charlie Riedel/AP hide caption

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Charlie Riedel/AP

Rep. John Dingell, D-Mich., the longest-serving member of Congress, is celebrated by colleagues, including Vice President Biden, on Capitol Hill in June 2013. A former chairman of the Energy and Commerce Committee, Dingell, now 87, announced in February that he will retire after this term. J. Scott Applewhite/AP hide caption

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J. Scott Applewhite/AP