Republican presidential candidate Sen. Rand Paul's 10 1/2 hours on the Senate floor were about liberty, the Constitution and the need to stand out in a field of presidential hopefuls. Andrew Harnik/AP hide caption

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A young female protester faces down armed police officers at an anti-Vietnam War demonstration outside the 1968 Democratic National Convention in Chicago. Hulton Archive/Getty Images hide caption

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Senate Minority Leader Harry Reid, D-Nev., (left) and Majority Leader Mitch McConnell, R-Ky., at a ceremony last month at the U.S. Capitol. Chip Somodevilla/Getty Images hide caption

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Hillary Clinton is running with all the advantages and challenges of someone who has been in the public eye for more than two decades. Andrew Burton/Getty Images hide caption

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Sen. Christopher Dodd, D-Conn., left, with then-Senate Minority Leader Tom Daschle at a 1995 news conference on Capitol Hill. Harry Reid took over as leader in 2005 after Daschle unexpectedly lost his re-election. At the time, Reid was unknown to most Americans, but he beat back a challenge Dodd. John Duricka/AP hide caption

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Vice President Biden and House Speaker John Boehner wait for President Obama's State of the Union address in front of a joint session of Congress in 2012. As vice president, Biden is also leader of the U.S. Senate, but only gets a vote when senators are evenly divided. Saul Loeb/AP hide caption

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Former Secretary of State and likely 2016 presidential candidate Hillary Clinton faces the media Tuesday over her use of a private server and email account she used to conduct public business. Richard Drew/AP hide caption

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Protesters filled Wisconsin's state Capitol in Madison on Monday, demonstrating against last weekend's shooting death of Tony Robinson, an unarmed black man. Andy Manis/AP hide caption

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President Obama arrives at the TransCanada Stillwater Pipe Yard in Cushing, Okla., in 2012 after renewed momentum in Congress to approve construction of the northern leg of the Keystone XL pipeline. Pablo Martinez Monsivais/AP hide caption

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