“If the party doesn’t change what they’re doing, we’re not going to take back the House, we’ll lose seats in the Senate and folks will come around after and say, ‘What happened?’” warned Representative Cedric L. Richmond of Louisiana, chairman of the Congressional Black Caucus. “We are doing a pathetic job of reaching out to minority voters.”

In both Alabama and Virginia, Democrats have tried to lay the groundwork for stronger black turnout in 2017 and midterms next year. Officials with the Democratic Congressional Campaign Committee briefed party strategists this month on plans to conduct research in several states, including New Jersey and Virginia, to identify issues most likely to motivate minority voting in 2018.

In Alabama, national leaders, including Senators Chuck Schumer and Bernie Sanders, have appealed to Mr. Woodfin to deploy his field organization to help Mr. Jones in the special election for the Senate.

Mr. Woodfin, a 36-year-old insurgent who toppled an incumbent Democrat this month, said he intended to help Mr. Jones, who convicted two Ku Klux Klansmen for a Civil Rights-era church bombing in his city. African-Americans are “looking for people to fight for their issues,” he said.

In Virginia, Mr. Northam has targeted black voters in the final weeks of the race, frequenting black churches and campaigning with Eric H. Holder Jr., the former attorney general, in addition to Mr. Obama.

But Mr. Northam’s overtures have been met with mixed results.

Kathy Harkless and two of her fellow congregants at First Mount Zion Baptist Church had just met Mr. Northam after he attended worship services here Sunday, but when asked about his bid for governor, they quickly steered the conversation toward Washington.

“I don’t want what we have now,” said Ms. Harkless, referring to Mr. Trump. “It’s awful.”

It is a familiar refrain to Dr. Luke E. Torian, who divides his time pastoring the church, founded 150 years ago by former slaves, and representing parts of this Washington exurb in the state legislature.