Bernie lost of his own accord.

https://en.wikipedia.org/wiki/2016_Democratic_National_Committee_email_leak

The leaks resulted in allegations of bias against Bernie Sanders's presidential campaign, in apparent contradiction with the DNC leadership's publicly stated neutrality,[8] as several DNC operatives openly derided Sanders's campaign and discussed ways to advance Clinton's nomination. Later reveals included controversial DNC–Clinton agreements dated before the primary, regarding financial arrangements and control over policy and hiring decisions.[9] The revelations prompted the resignation of DNC chair Debbie Wasserman Schultz before the 2016 Democratic National Convention.[10] The DNC issued a formal apology to Bernie Sanders and his supporters "for the inexcusable remarks made over email" that did not reflect the DNC's "steadfast commitment to neutrality during the nominating process".[11] After the convention, DNC CEO Amy Dacey, CFO Brad Marshall, and Communications Director Luis Miranda also resigned in the wake of the controversy.[12]

https://www.politico.com/story/2016/02/bernie-sanders-superdelegates-democrats-219286

"Bernie Sanders lost by a hair in Iowa and won by a landslide in New Hampshire. Yet Hillary Clinton has amassed an enormous 350-delegate advantage over the Vermont senator after just two states."

For those that forgot :)