Rep. John Dingell, seen here in June, was admitted to a hospital Friday as a precautionary measure. The Democrat is retiring as the longest-serving member of Congress in U.S. history. Mark Wilson/Getty Images hide caption

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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

itoggle caption J. Scott Applewhite/AP

Debbie Dingell with Michigan Sen. Carl Levin and then-presidential candidate Barack Obama during a 2008 campaign event in Flint, Mich. Dingell is expected to announce Friday that she will run for her husband's House seat. Alex Brandon/AP hide caption

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Rep. John Dingell, D-Mich., whose House career stretches nearly 60 years, will retire at the end of his term as the longest-serving member of Congress in history. Manuel Balce Ceneta/AP hide caption

itoggle caption Manuel Balce Ceneta/AP