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WASHINGTON, DC - JULY 30: Democratic U.S. presidential hopeful and U.S. Sen. Bernie Sanders (I-VT) listens during a forum July 30, 2015 on Capitol Hill in Washington, DC. Sen. Sanders held the forum to discuss "The Debt Crisis in Greece and Beyond." (Photo by Alex Wong/Getty Images)
WASHINGTON, DC - JULY 30: Democratic U.S. presidential hopeful and U.S. Sen. Bernie Sanders (I-VT) listens during a forum July 30, 2015 on Capitol Hill in Washington, DC. Sen. Sanders held the forum to discuss "The Debt Crisis in Greece and Beyond." (Photo by Alex Wong/Getty Images)

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