It is a region of small, postindustrial cities that have suffered manufacturing losses, where largely white voters, after years of voting for Democrats, embraced Mr. Trump’s nationalism and culturally backward-gazing message.

“You can look at the part of the country where I live and where I serve, there is a feeling they have been left behind and we haven’t delivered,” said Representative Cheri Bustos, a Democrat whose northwest Illinois district includes nine Obama-Trump counties. All of them stayed with Mr. Trump this year.

Ms. Bustos, who was chair of the Democrats’ House campaign committee, barely won re-election herself. She said Democrats needed to bring concrete benefits to farmers in the same way Franklin D. Roosevelt delivered rural electrification.

Despite expectations that Mr. Biden, with his Everyday Joe persona, would win back many blue-collar voters, he appears to have done worse with them than Hillary Clinton or Mr. Obama in both of his elections.

Suburbia and beyond: Pivot counties that flipped to Biden

Some of the 25 pivot counties that Mr. Biden did flip back reflect gains he made in suburbs across the country — the key to his election — or are in states like Pennsylvania, where his campaign poured in resources for advertising and voter outreach.

Four of these “boomerang” counties, to use the term favored by Ballotpedia, were in Minnesota. Each has a small or medium-size city that is an island of blue voters in a sea of red ones. Unlike in 2016, when complacency, lack of enthusiasm for the Democratic nominee and third-party candidates all cut into votes for Mrs. Clinton, this year there was a surge of Democratic turnout in the state, which Mr. Biden won by 7.1 points, compared with Mrs. Clinton’s 1.5-point margin in 2016.

In Clay County, one of the four pivot counties in Minnesota that Mr. Biden wrangled back from Mr. Trump, Mr. Biden won 3,500 more votes than Mrs. Clinton did in 2016. Mr. Trump increased his total by a more modest 1,500.