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Open Image ModalDemocratic presidential candidates Hillary Clinton and Bernie Sanders participate in the debate hosted by NBC News and YouTube on Jan. 17, 2016, in Charleston, South Carolina. (credit:Andrew Burton/Getty Images)
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Open Image ModalDemocratic presidential candidates Hillary Clinton and Bernie Sanders greet the audience before the PBS NewsHour Presidential Primary Debate in Milwaukee, Wisconsin, on Feb. 11, 2016. (credit:Tasos Katopodis/AFP/Getty Images)
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Open Image ModalHillary Clinton speaks during a campaign event in Portsmouth, New Hampshire, on Feb. 6, 2016. (credit:Daniel Acker/Bloomberg via Getty Images)
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Open Image ModalDemocratic presidential candidate Hillary Clinton listens as Bernie Sanders speaks during the MSNBC Democratic debate at the University of New Hampshire in Durham on Feb. 4, 2016. (credit:Jewel Samad/AFP/Getty Images)
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Open Image ModalDemocratic presidential candidates Bernie Sanders and Hillary Clinton participate in the PBS NewsHour Democratic presidential candidate debate at the University of Wisconsin-Milwaukee on Feb. 11, 2016. (credit:Win McNamee/Getty Images)
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Open Image ModalDemocratic presidential candidate Bernie Sanders listens as Hillary Clinton (not in picture) speaks during the MSNBC Democratic debate at the University of New Hampshire in Durham on Feb. 4, 2016. (credit:Jewel Samad/AFP/Getty Images)
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Open Image ModalDemocratic presidential candidates Bernie Sanders and Hillary Clinton participate in the PBS NewsHour Democratic presidential candidate debate at the University of Wisconsin-Milwaukee on Feb. 11, 2016. (credit:Win McNamee/Getty Images)
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Open Image Modal Democratic presidential candidates Hillary Clinton and Bernie Sanders field questions from moderators Lester Holt and Andrea Mitchell (right) during the Democratic debate hosted by NBC News and YouTube on Jan. 17, 2016, in Charleston, South Carolina. (credit:Andrew Burton/Getty Images)
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Open Image ModalDemocratic presidential candidate Hillary Clinton speaks to supporters during her caucus night event in the Olmsted Center at Drake University on Feb. 1, 2016, in Des Moines, Iowa. (credit:Win McNamee/Getty Images)
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Open Image ModalDemocratic presidential candidates Hillary Clinton and Bernie Sanders participate in the MSNBC Democratic debate at the University of New Hampshire in Durham on Feb. 4, 2016. (credit:Jewel Samad/AFP/Getty Images)
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Open Image ModalDemocratic presidential candidates Bernie Sanders and Hillary Clinton participate in the PBS NewsHour Democratic presidential candidate debate at the University of Wisconsin-Milwaukee on Feb. 11, 2016. (credit:Win McNamee/Getty Images)
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Open Image ModalDemocratic presidential candidate Bernie Sanders speaks at the New Hampshire Democratic Party\'s 2016 McIntyre Shaheen 100 Club Celebration on Feb. 5, 2016. (credit:Andrew Burton/Getty Images)
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Open Image ModalDemocratic presidential candidate Bernie Sanders and Hillary Clinton participate in the PBS NewsHour Democratic presidential candidate debate at the University of Wisconsin-Milwaukee on Feb. 11, 2016. (credit:Win McNamee/Getty Images)
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Open Image ModalDemocratic presidential candidates Hillary Clinton and Bernie Sanders chat following the Democratic debate hosted by NBC News and YouTube on Jan. 17, 2016, in Charleston, South Carolina. (credit:Andrew Burton/Getty Images)
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Open Image ModalDemocratic presidential candidate Hillary Clinton speaks at the MSNBC Democratic debate at the University of New Hampshire on Feb. 4, 2016, in Durham, New Hampshire. (credit:Justin Sullivan/Getty Images)
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Open Image ModalDemocratic presidential candidates Hillary Clinton and Bernie Sanders shake hands as they participate in the MSNBC Democratic debate at the University of New Hampshire in Durham on Feb. 4, 2016. (credit:Jewel Samad/AFP/Getty Images)
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Open Image ModalCandidates Hillary Clinton and Bernie Sanders gesture during the Democratic presidential candidate debate in Charleston, South Carolina, on Jan. 17, 2016. (credit:Patrick T. Fallon/Bloomberg via Getty Images)
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Open Image ModalDemocratic presidential candidates Hillary Clinton and Bernie Sanders shake hands before participating in the MSNBC Democratic debate at the University of New Hampshire in Durham on Feb. 4, 2016. (credit:Jewel Samad/AFP/Getty Images)