WASHINGTON — (CNN) Bernie Sanders is back on the stump.

The independent senator from Vermont, who has emerged as a party leader in the aftermath of Hillary Clinton’s defeat last week, said Thursday that progressives must dedicate themselves to winning over voters who turned to Donald Trump on Election Day.

In a speech to hundreds of supporters and activists gathered on a chilly fall afternoon in Washington, Sanders pinned Trump’s victory on the Democratic establishment’s failure to engage with millions of Americans who feel forgotten by political leaders and hemmed in by stagnant local economies.

“The party has got to recognize some very important realities that Donald Trump, in fact, recognized,” Sanders said, keeping up a drumbeat he began last week in a New York Times op-ed and has returned to in a round of subsequent appearances. “And that is, yes, we are better off today economically than we were eight years ago, we’ve made a lot of progress in a lot of areas. But there are millions and millions of people today, working-class people, middle-class people, who are living in despair. And we have got to recognize that reality.”

Sanders campaigned heartily for Clinton after she clinched the Democratic nomination this summer, but as the American left begins to consider its options in the wake of a slow-building electoral wipeout — Republicans now control the White House, both chambers of Congress, and dominate state politics — he and the movement that fueled his campaign are moving quickly to grab hold of the party.

“There is a lot of pain in America,” Sanders said in a short speech just a few hundred feet from his Senate office. “Capitol Hill doesn’t understand it — we do. And we are going to reach out to those brothers and sisters (who voted for Trump) and work with them.”

The organizers behind the rally, which was planned months before the election and initially slated as a demonstration against the the 12-nation Trans-Pacific Partnership, a pact President Barack Obama has championed but has been rejected by many progressives who are leery of expansive free trade bill. But as if to further underscore the odd, partisan-defying moment, the deal is now all but dead — thanks in large part to Trump’s opposition.

Activists in Upper Senate Park on Thursday wrestled with the irony, some by arguing that the President-elect had hijacked the economic populist movement they had resurrected.

[van id=”politics/2016/11/18/bernie-sanders-still-feels-the-bern-origwx-allee.cnn”]

“TPP was stopped because of you and Donald Trump had nothing to do with it,” Tefere Gebre, the executive vice president of the AFL-CIO, told the crowd. “Working together, we made the TPP toxic for politicians. Then opportunistic politicians tried to jump on the bandwagon and say, ‘I was there too.'”

Rep. Rosa DeLauro, a Connecticut Democrat and Sanders ally, congratulated activists on defeating a wide range of “forces arrayed against us,” including “financial institutions, the Business Roundtable, the Chamber of Commerce, the president of the United States, pharmaceutical industries, and big agriculture industries.”

“They thought we couldn’t do it,” she said, “but we certainly showed them.”

Before former Ohio state senator Nina Turner took the stage to begin emceeing duties, RoseAnn DeMoro, the executive director of National Nurses United, confessed she and the group, which organized the event, had not expected such a swift or politically confounding victory.

“I wasn’t anticipating this and I wasn’t thinking of this when we planned the rally,” she said, “but we’re very, very excited about (the turnout). Millions of people want to engage. We’re not seeing a falloff in terms of energy.”

On the same afternoon Ohio Rep. Tim Ryan formalized his plans to challenge to Democratic House Minority Leader Nancy Pelosi, DeMoro argued that the power center in liberal politics had already shifted — and that while Sanders stood as progressives’ “fundamental leader,” it would not rely on him for direction at every step.

“(Sanders) has has millions looking to him for hope and direction — he’s critical,” she said. “Having said that, the movie was there before Bernie. Bernie was able to galvanize the movement. The movement got much, much stronger. So while Bernie is critical, the movement exists, the movement has a life of its own.”

Two hours later, a group of about 25 union nurses walked a half-mile south to the Longworth House Office Building, passed through metal detectors, took elevators to the second floor, and gathered around the entryway to House Speaker Paul Ryan’s office.

With a letter — and piece of pie — in hand, they asked a staffer if Ryan was available to discuss their opposition to his longstanding plans to remake Medicare.

“Paul is not here right now,” he informed them politely, and then after exchanging contact information, closed the heavy wood door behind him.

The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: CNN)