While Clinton increased her delegate lead over Sanders to 1,052 to to 427—2,383 delegates are needed to win the nomination—Nicholas Confessore reports for The New York Times that one concern could be that "Democratic turnout has fallen drastically since 2008, the last time the party had a contested primary, with roughly three million fewer Democrats voting in the 15 states that have held caucuses or primaries through Tuesday, according to unofficial election results tallied through Wednesday afternoon."
Voting "declined in almost every state, dropping by roughly 50 percent in Texas and 40 percent in Tennessee," Confessore writes. "In Arkansas, Alabama and Georgia, the number of Democrats voting decreased by between a quarter and a third. The falloff in Democratic primary turnout—which often reveals whether a candidate is exciting voters and attracting them to the polls—reached deep into some of the core groups of voters Clinton must not only win in November, but turn out in large numbers. It stands in sharp contrast to the flood of energized new voters showing up at the polls to vote for Donald J. Trump in the Republican contest."
"Some Democrats now worry that Clinton will have difficulty matching the surge in new black, Hispanic and young voters who came to the polls for President Obama in 2008 and 2012," Confessore writes. Cornell Belcher, a Democratic pollster who worked on Obama’s re-election campaign, told Confessore, “Barack Obama without that surge is John Kerry. Just turning out the traditional minority base is not a 51 percent pathway going into November.”