In Ohio, Senator Sherrod Brown, a longtime champion of working-class voters, was toppled by a rich Republican former car dealer.

In Washington, President Biden — who won the Democratic nomination four years ago with the help of blue-collar voters — must now hand back power to Republicans and surrender leadership of a party increasingly dominated by highly educated voters.

And in Pennsylvania, Senator Bob Casey, whose family name has for years been synonymous with white working-class Democrats, is confronting the real possibility of defeat.

Eight years after fury among white working-class voters propelled Donald J. Trump to victory, Democrats swore that this time, they would try to do better with that group.

Instead, the party’s staggering challenges with blue-collar voters have only worsened. Widespread frustration with high prices and alienation from Democrats have turned the party’s lawmakers in Trump territory into an ever-more-endangered species.

“When the change doesn’t show up, the hope for change turns into anger,” said Representative Matt Cartwright, a battle-tested Pennsylvania Democrat from the Scranton area who narrowly lost this month. “The anger showed up.”