Michael Barone writes in the Washington Examiner,
Two decades ago, lots of self-described moderates and even conservatives voted in Democratic primaries. Not so these days. The slump in Democratic primary and caucus turnout, from 38 million in 2008 to 31 million in 2016, was due to a sharp decline in turnout by self-described moderates.
Hillary Clinton's move from her husband's 1990s triangulation to her near-total acceptance this year of Bernie Sanders's left-wing platform was a rational response to changes in the Democratic primary electorate.