The Vermont senator declined to criticize his primary rival, Hillary Clinton, attributing Tuesday's election loss to a "lack of enthusiasm" among Democrats. "People just did not come out to vote," he said.
He said he would support Rep. Keith Ellison of Minnesota to become the next chairman of the Democratic National Committee.
Sanders endorsed Clinton after their lengthy primary and campaigned extensively for her. He said she's had "an exemplary political career. She has served the public for many, many decades and has broken many barriers," adding that "she deserves an enormous amount of credit. She worked extraordinarily hard in this campaign."
But he said the party as a whole was unable to make a strong enough case to struggling workers, particularly in the industrial Midwest, who sided with Trump.
"You cannot be a party which on one hand says we're in favor of working people, we're in favor of the needs of young people but we don't quite have the courage to take on Wall Street and the billionaire class. People do not believe that. You've got to decide which side you're on."
While he said he was hopeful he would be able to work with the incoming Trump administration, he made clear that would not be likely.
"I hope I'm wrong, but I believe that he is a fraud, and I think despite all of his rhetoric about being a champion of the working class, it will turn out to be hollow," Sanders said of the president-elect.
Sanders said he had not yet considered whether to seek a leadership position within the Senate Democratic caucus and was expected to become the top Democrat on either the Budget Committee or another post. But he said he would seek to mobilize Democrats to help the party rebuild.
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