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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Democratic presidential candidate Hillary Clinton is facing questions about money, access and influence while she was secretary of state. Jacquelyn Martin/AP hide caption

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Hillary Clinton addresses the Pennsylvania AFL-CIO three weeks before the Democratic primary contest against Barack Obama. Seated at right is Pennsylvania AFSCME President Gerald W. McEntee. Charles Dharapak/AP 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 begins to speak as her husband, former President Bill Clinton, moves to take a seat after introducing her at the Clinton Global Initiative on Sept. 22, 2014, in New York. Mark Lennihan/AP 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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"Who, me? Run?" Would-be presidential candidates are ditching "testing the waters" and "exploratory committees" to hold onto unlimited and undisclosed cash for longer. LA Johnson/NPR 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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