BURLINGTON, Vt. — Senator Bernie Sanders has canceled a planned rally in Jackson, Miss., and will instead travel to Michigan on Friday, a striking indication that his presidential campaign is shifting its focus to the Midwest and largely ceding another Southern state to former Vice President Joseph R. Biden Jr., according to people familiar with the plans.
After holding a rally in Phoenix on Thursday night, Mr. Sanders had been scheduled to travel to Jackson on Friday for a rally focused on racial justice.
The change in plans suggests that Mr. Sanders will not challenge Mr. Biden for the support of black voters in the South — a vital base in the Democratic Party — and is instead going all-in on the Midwest as he tries to compete with Mr. Biden for working-class voters there. Black voters in the South have overwhelmingly backed Mr. Biden to this point, and on Super Tuesday this week their support lifted him in states like Alabama, North Carolina and Virginia.
In Alabama, Mr. Sanders won only 9 percent of black voters, compared with 72 percent for Mr. Biden, according to exit polls. Mr. Biden outperformed Mr. Sanders among black voters in Virginia by more than 50 points, and by 40 points or more in Texas and North Carolina. In several states, Mr. Sanders came in third among black voters, behind not only Mr. Biden but also Michael R. Bloomberg.
Mr. Bloomberg quit the race a day later, and Mr. Sanders’s ideological rival on the left, Senator Elizabeth Warren, announced on Thursday that she was dropping out as well, effectively making the Democratic contest a two-man race between Mr. Sanders and Mr. Biden.
The shift in Mr. Sanders’s schedule was also an acknowledgment that he had not improved his standing among black voters in the South four years after his first run for president. In 2016, he faced criticism for his inability to organize support from African-Americans, a weakness that contributed to his loss to Hillary Clinton in the Democratic primary.
Speaking to reporters in Burlington on Thursday, Mr. Sanders acknowledged the scheduling change but said his campaign was sending staff members to Mississippi, which votes next Tuesday, along with Michigan and four other states. Michigan is the biggest prize of that day, awarding more than three times the pledged delegates of Mississippi.
“If possible, I will try to get to Mississippi,” Mr. Sanders said. “You can’t go every place.”
“We’re very proud of the fact that we have strong support in the African-American community,” he added. “We are going to be working with the African-American community, the Muslim community, in Michigan, and in every state in the country.”
Asked if he saw a path forward for his campaign without winning Michigan, Mr. Sanders said he did. “Every state is important,” he said. “Michigan is very, very important.”
He also acknowledged Ms. Warren’s exit from the race, crediting her with running a “strong, issue-oriented campaign” that “changed political consciousness in America.”
“I would simply say to her supporters out there, of whom there are millions, we are opening the door to you, we would love you to come on board,” Mr. Sanders said. “Together I think we can win this primary process.”
Sanders aides are confident that Mr. Sanders lines up favorably against Mr. Biden in the industrial Midwest, and they have already laid out plans to highlight Mr. Biden’s record on trade, which includes voting for the North American Free Trade Agreement. While many blue-collar voters say they feel a connection to Mr. Biden, many have also grown increasingly suspicious of free trade in the Trump era.
In an interview, Faiz Shakir, the campaign manager for Mr. Sanders, said the campaign was considering running an ad in Midwestern states like Michigan and Ohio that will emphasize Mr. Biden’s record on trade, and Mr. Sanders has already added blistering remarks about Mr. Biden into his stump speech.
“I will be talking in Michigan about the fact that Joe supported disastrous trade agreements,” Mr. Sanders said Thursday.
At an event in Phoenix on Thursday night, his first rally since Super Tuesday, Mr. Sanders laced into Mr. Biden for his record on trade, the Iraq war and Social Security, as he has done recently.
But he also opened two new lines of attack, knocking Mr. Biden for his past votes for the “don’t ask, don’t tell” policy that prohibited openly gay people from serving in the military and for his past support for the Hyde Amendment, a measure that bans federal funding for most abortions.
“When you’ve got two candidates, unlike when you have 18 candidates, it is possible to really contrast the views of the candidates,” Mr. Sanders said. “That’s what I’m going to do.”
There was a brief disruption at the rally in Phoenix when a man in the crowd unfurled a Nazi flag bearing a swastika, before he was quickly removed. “The senator is aware of the flag with the swastika on it and is disturbed by it,” said Mike Casca, a campaign spokesman. Mr. Sanders is Jewish.
A crucial part of Mr. Sanders’s argument has been the idea that he is the most electable candidate, able to defeat President Trump in a general election by appealing to the same working-class white voters who helped hand Mr. Trump his victory in 2016. But among aides and advisers, there has been a growing recognition that his claim hinges on his ability to demonstrate this strength in Midwestern states during the primary.
Mr. Sanders’s disappointing performance on Super Tuesday — he won only four states to Mr. Biden’s 10 — has only increased the sense of urgency inside his campaign.
At a news conference on Wednesday, Mr. Sanders said he was “disappointed” in the Super Tuesday results. And in an extraordinary concession, he admitted that his campaign had not managed to generate the soaring turnout among young people that he had banked on to secure the nomination.
While Mr. Sanders has managed to draw support in high numbers among other demographic groups, including Latino voters, his deficit with black voters in the South was central to his losses on Super Tuesday.
Rather than cite his own shortcomings, however, Mr. Sanders has pointed to his opponents’ strong connections with African-American voters. In an interview on Wednesday night with Rachel Maddow of MSNBC, he suggested that Mr. Biden was benefiting from his relationship with former President Barack Obama — and used a parallel argument to explain his deficit in 2016 as well.
“We’re running against somebody who has touted his relationship with Barack Obama for eight years,” Mr. Sanders said. “Barack Obama is enormously popular in this country in general and the African-American community. Running against Hillary Clinton, Bill Clinton was enormously popular.”
“It’s not that I’m not popular,” he added. “Biden is running with his ties to Obama and that’s working well.”
He also said he was generally doing well among voters of color, including Latinos, and with younger black voters.