US Democratic presidential candidates Hillary Clinton (L) and Bernie Sanders shake hands before the CNN Democratic Presidential Debate at the Brooklyn Navy Yar on April 14, 2016, in New York. 
Hillary Clinton and Bernie Sanders take their increasingly acrimonious battle for the Democratic White House nomination to a debate stage in Brooklyn  ahead of the key New York primary. / AFP / Jewel SAMAD        (Photo credit should read JEWEL SAMAD/AFP/Getty Images)