Sen. Marco Rubio, R-Fla, is among a bipartisan group of eight senators who this week announced a plan to overhaul the nation's immigration laws. Charlie Neibergall/AP hide caption

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Energy Secretary Steven Chu tours the Vogtle nuclear power plant in Waynesboro, Ga., last year. David Goldman/AP hide caption

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Republican Scott Brown, shown here on Capitol Hill in 2010 not long after coming to the Senate in a special election, announced Friday that he won't run in this year's special election in Massachusetts to replace Democrat John Kerry. Mark Wilson/Getty Images hide caption

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New York Mayor Ed Koch raises his arms in victory on Sept. 11, 1985, after winning the Democratic primary in his bid for a third four-year term. Mario Suriani/AP hide caption

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Secretary of State Hillary Clinton at a town hall meeting on Tuesday in Washington, D.C. She officially leaves her post on Friday. Mandel Ngan/AFP/Getty Images hide caption

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Secretary of Defense nominee Chuck Hagel testifies Thursday before the Senate Armed Services Committee during his confirmation hearing. Alex Wong/Getty Images hide caption

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