New York City Mayor Bill de Blasio is set to step onto the national stage with his progressive "Contract With America." Seth Wenig/AP hide caption

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Former President Bill Clinton campaigns before the 2014 elections for former Sen. Mark Pryor, center, and Mike Ross, right, the Democratic candidate for governor. Justin Sullivan/Getty Images hide caption

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Sen. Bernie Sanders, I-Vt., speaks at a rally demanding presidential action to raise the minimum wage to $15 an hour. Sanders will run to Hillary Clinton's left, trying to elevate economic issues. Win McNamee/Getty Images hide caption

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Hillary Clinton's campaign logo was changed Tuesday to show support for same-sex marriage on the day of oral arguments at the Supreme Court. Hillary Clinton campaign hide caption

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Former Secretary of State Hillary Clinton speaks at the Clinton foundation's Clinton Global Initiative conference with her husband, Bill, and daughter, Chelsea, looking on. Michael Loccisano/Getty Images hide caption

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President Obama talks with Malaysian Prime Minister Najib Razak at the East Asia Summit in Myanmar in November. Obama is trying to strike a 12-country Trans-Pacific Partnership, which would include Malaysia. Christophe Archambault/AFP/Getty Images hide caption

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Former Maryland Gov. Martin O'Malley, a Democrat who is considering a 2016 presidential campaign, is interviewed by NPR's Steve Inskeep. Ariel Zambelich/NPR hide caption

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Reporters and campaign staffers rush to their cars to get to Hillary Clinton's first Iowa campaign stop. Tamara Keith/NPR 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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Hillary Clinton has described herself as the most famous person you don't really know. And as she launches into her second presidential campaign, she'll be reintroducing herself to voters who largely think they have her figured out. Mel Evans/AP hide caption

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Hillary Clinton in June 1969 at the Rodham family home. She was featured in a Life magazine story called "The Class of '69." Lee Balterman/The LIFE Premium Collection/Getty Images hide caption

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Sen. Elizabeth Warren talked about 2016 to WBUR's Here & Now: "What I care about is that everyone who runs for president, who runs for any national office right now, talks about this core set of issues." Manuel Balce Ceneta/AP hide caption

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Sen. Charles Schumer of New York stands a podium March 3 as Senate Minority Leader Harry Reid of Nevada looks on. Reid is backing Schumer to be his replacement as Democratic leader. J. Scott Applewhite/AP hide caption

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