LOS ANGELES—On a crisp November evening three weeks after the election, about 600 local activists gathered on a sound stage at the old Mack Sennett studios in Silver Lake where nearly a century ago the Keystone Cops slipped on banana peels and dodged pies in the face. These avatars of Hollywood liberalism had just suffered a similar humiliation and had come to figure out how to pick themselves up and start all over again in Donald Trump's America.

The crowd, which quickly overflowed the available seats and sat on the bare floor, had been convened by Beau Willimon, the creator of the Netflix series "House of Cards," and a still-idealistic veteran of Howard Dean's insurgent 2004 presidential campaign. As Willimon took the microphone, a gray scrim hanging behind him bore the projected exhortation: SIGN UP— ACTIONGROUPS.NET, a pitch for Willimon's informal network of grass-roots efforts. The disheartened but tentatively defiant message of the evening: "I won't quit—if you don't quit."

It was not supposed to be like this, a defeated army sitting on the floor of an empty sound stage grasping for a chance at political impact. This was the class of people who were supposed to have a reserved seat at the table at Hillary Clinton's first White House Correspondents' Dinner. Now, like the deep-pocketed celebrities and industry titans who by one reliable estimate had raised some $60 million for her candidacy here, they were suddenly out in the cold. On the floor.

The new relationship between Hollywood and the incoming White House was on stark display this month when Meryl Streep took to the stage at the Golden Globes to say—without naming the incoming president—that Trump's mocking of a disabled reporter "broke my heart," and Trump fired back in the New York Times and on Twitter, calling the three-time Oscar winner "one of the most over-rated actresses in Hollywood," and just another of the "liberal movie people" he'd expect to attack him.

Zip Code 90210 and environs has long been one of the Democratic Party's most reliable ATM branches, the town where rich liberals can feel better about being rich by contributing to causes that prove their liberal bona fides and let them rub shoulders with real power. Celebrities like Magic Johnson, Seth MacFarlane, Lionel Richie and George Clooney—together with moguls like Jeffrey Katzenberg, Bob Iger, Haim Saban, Barry Diller and Michael Eisner—had held dozens of fundraisers for Clinton, or entertained for free to support her, over the past two years.