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DENVER, CO - FEBRUARY 13: A supporter hoists a campaign sign as Democratic Presidential candidate Bernie Sanders (D-VT) speaks to the crowd at a rally on February 13, 2016 in Denver, Colorado. Sanders spoke about keeping big money out of politics, climate change and making college affordable and drew an overflow crowd. (Photo by Marc Piscotty/Getty Images)

DENVER, CO - FEBRUARY 13: A supporter hoists a campaign sign as Democratic Presidential candidate Bernie Sanders (D-VT)  speaks to the crowd at a rally on February 13, 2016 in Denver, Colorado. Sanders spoke about keeping big money out of politics, climate change and making college affordable and drew an overflow crowd. (Photo by Marc Piscotty/Getty Images)