Bernie Sanders thinks he has a pretty good idea why Hillary Clinton and Democrats lost in the 2016 election.

"Look, you can't simply go around to wealthy people's homes raising money and expect to win elections," the Vermont senator, who gave Clinton a surprisingly strong run for the Democratic nomination, told NPR's David Greene in an interview airing on Morning Edition. "You've got to go out and mix it up and be with ordinary people."

That picks up on a criticism of Clinton devoting too much time to fundraising — and not enough to on-the-ground campaigning in traditionally Democratic states, like Michigan and Wisconsin. In the general election, Clinton never visited Wisconsin after she became the nominee and visited Michigan late in the game. The two Upper Midwestern states swung narrowly to Trump: Wisconsin by slightly more than 20,000 votes and Michigan by slightly more than 10,000. During the primary, Sanders boasted of his small-donor donations.

"The Democratic Party swallowed the bait," he argued. "They became hooked on big money."

The Vermont senator added that he believes Democrats have lost touch with the needs of everyday Americans.

"I happen to believe that the Democratic Party has been not doing a good job in terms of communicating with people in cities, in towns and in rural America, all over this country," he said.

Some have blamed Sanders, in part, however for Clinton's loss. Young voters were drawn to his campaign, but many chose a third-party candidate in the general election. Although Sanders campaigned for Clinton, at times he had a hard time voicing full-throated support for her.

The kind of harsh criticism he leveled of Clinton on her Wall Street speeches and decrying her as part of the status quo, rather than building up her beliefs and policies (that certainly stand in stark contrast to Donald Trump) has irked party loyalists.

That's especially true, considering that although Sanders ran in the Democratic primary and caucuses with Democrats, he has declined to put the "D" next to his name. He is back in the Senate as an independent.

Sanders believes Trump's message resonated with workers, like the ones in Wisconsin and Michigan, who were hit hard by the economic recession and haven't yet recovered. It was a connection Democrats were largely unable to maintain.

"One of the reasons that Mr. Trump won is that we have millions of people who have given up on the political process, who don't believe that Congress is listening to their pain," Sanders said. "What the Democratic Party has got to do is start listening."

In that way, Trump and Sanders are alike. Both tapped into the anti-establishment current that permeated the 2016 election. When asked if he thought he would have been able to win the general election against Trump, Sanders brushed it off.

"I don't think it helps to relive history," said Sanders, whose campaign team touted polling during the primary that showed him faring better against Trump in head-to-head matchups. "The answer is I don't know. Nobody knows. It's not worth speculating about. We are where we are."

Sanders sees Trump's anti-establishment tendencies as a potential opportunity, at least when it comes to the fight to preserve Medicare and Medicaid.

Trump promised repeatedly throughout the campaign that he would not cut Medicare, Medicaid or Social Security if elected. Sanders wants to hold Trump accountable for that promise, regardless of what Republicans in Congress want to do.

Sanders says Trump has a choice: "Either he can have the courage and get up in front of the American people, or do it through a tweet, and say, 'You know what? Hey, I was just kidding. I was really lying.'"

Or Trump can tell his fellow Republicans that they're wasting their time on legislation that cuts those programs. "That would be the right thing to do," Sanders said. "And I look forward to Trump telling the American people that that is what he intends to do."

To press the issue, Sanders, along with congressional leaders, is calling on his colleagues to organize Jan. 15 rallies protesting threats to the Affordable Care Act, Medicare and Medicaid.

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