A recurring argument I’ve heard (several times, in various ways) from Sanders supporters runs something like this:
Hillary Clinton’s historically high unfavorables will depress turnout among Democratic base voters in the general election, especially the progressive wing of the party. We need someone like Bernie Sanders to generate unprecedented turnout among hitherto underrepresented electoral constituencies in order to win the White House in 2016.
It is a plausible enough argument—especially early on in the primaries—but by now we should already know whether it has proven true when tested in the field in states where actual Democratic voters had the chance to actually cast votes. If the argument is sound, we should expect that Clinton will have been swamped by an influx of Sanders voters in the relatively few swing states which will most likely decide the presidential election this fall.
The “swingingest” states this year are (from west to east) Nevada, Colorado, Iowa, Wisconsin, Florida, Ohio, North Carolina, Virginia, Pennsylvania, and New Hampshire. Here is what the primaries and caucuses looked like, in chronological order:
Clinton is driving far more voters to the polls overall; the only primary contest states where Sanders clearly outperforms her are New Hampshire (4 electoral votes) and Wisconsin (10 electoral votes). Arguably, Sanders could turn out more people in Colorado as well, but caucus turnout is not a reliable indicator of voter turnout at the ballot box, as we saw dramatically demonstrated in the bizarre case of Nebraska, where they held both caucuses and primaries this year.
Turning out the base will indeed form a crucial component of the 2016 presidential contest, especially in high-population swing states such as Florida (29 electoral votes), Pennsylvania (20 electoral votes), Ohio (18 electoral votes), North Carolina (15 electoral votes), and Virginia (13 electoral votes). The data do not support the hypothesis that the Bernie Sanders movement has created a formidable turnout machine in those crucial areas.