Progressives took different lessons from the results, rejecting the idea that they were a harbinger of trouble for more liberal candidates like Senators Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts. Adam Green, a co-founder of the Progressive Change Campaign Committee, said it was “a completely made-up narrative that there’s any similarity between this very unique U.K. election and the dynamics in this country.”

Waleed Shahid, the spokesman for Justice Democrats, a progressive organization that backed Representative Alexandria Ocasio-Cortez of New York — she shared a video from Labour on Twitter on Thursday — and other liberal Democrats in 2018, argued that Mr. Corbyn’s defeat was a different kind of warning sign: that Democrats must focus more on working-class candidates in 2020.

“The lesson for the entire Democratic Party coalition: Across the Western world, center-left parties are bleeding voters in postindustrial places to the right wing or to not voting at all,” Mr. Shahid said. “That’s a serious development that’s happening all over the Western world.”

Both Mr. Biden and Mr. Sanders are especially strong with working-class voters, polls show.