In the heart of working-class Queens, Zohran Mamdani, the newly minted Democratic nominee for mayor of New York City, received polite applause as he stepped to the pulpit before a recent Sunday audience at an African Methodist Episcopal church.

He praised the rich history of the Greater Allen A.M.E. Church, and that of a former senior pastor who was also a congressman and prominent academic. And then he turned to his objective that day: preaching his political message to the largely unconverted.

Just over one-third of voters in the church’s corner of Southeast Queens supported Mr. Mamdani, according to precinct data from the June 24 primary, a signal that he has much work to do in predominantly Black neighborhoods.

Indeed, when Mr. Mamdani, a 33-year-old state assemblyman, spoke of his plans to freeze rents in rent-stabilized apartments, audible whispers and groans could be heard from the parishioners, many of them homeowners.

In his landmark victory in the Democratic primary, Mr. Mamdani was able to assemble a diverse alliance that included people who had voted for President Trump, immigrants, infrequent voters and newly registered ones. It did not, however, appear to include a majority of Black voters — a traditional requisite for any citywide Democratic candidate.

The ability of Mr. Mamdani, who is Indian American, to easily win without winning the Black vote marked a shift in the city’s political landscape, scrambling traditional assumptions about New York’s Black electorate and the influence it holds in city politics.

Black voters may yet follow decades of precedent and coalesce behind the Democratic nominee in November, but they will have other familiar Democrats to consider on third-party lines: Andrew M. Cuomo, the former governor, and Mayor Eric Adams, the city’s second Black mayor.

In the city’s predominantly Black precincts — those where more than four out of five people are Black — Mr. Mamdani earned less than 30 percent of the vote, an analysis by The New York Times found. And he lost in the wider swath of majority-Black precincts across the city, where he received only 42 percent of the vote.

Conversely, in neighborhoods where the Black population decreased the fastest between the 2010 and 2020 censuses, Mr. Mamdani won more than two out of every three votes.

Those rapidly changing neighborhoods include central Harlem in Manhattan and Fort Greene and Crown Heights in Brooklyn — suggesting that the city’s electoral map has been altered by decades of displacement from historically Black neighborhoods. Once, they could have been considered Mr. Cuomo’s strongholds. Now, after years of gentrification, they love Mr. Mamdani.

“The gentrification is now culminating in political erasure, and that is the kind of truth that has sent everyone into a tailspin trying to figure out what’s the new landscape,” said Anthonine Pierre, director of the Brooklyn Movement Center.

But even if Mr. Mamdani wins in November without capturing the majority of Black voters, he has made it clear that, as mayor, he will value their input.

“I will govern with a simple goal: to make this city affordable and to make a good and dignified life possible for each and every New Yorker,” he said to the churchgoers in Queens. “And what I ask of you is to hold me accountable in that promise.”

Afua Atta-Mensah, political director for Mr. Mamdani, said in a statement that the campaign is “deepening our support in Black communities by meeting with trusted leaders to grow awareness of our affordability agenda, which includes expanding Black homeownership, lowering immediate costs, and halting the exodus of Black New Yorkers from the neighborhoods they built.”

Still, the varied responses to Mr. Mamdani’s victory among Black voters and leaders have highlighted new fault lines among one of the city’s most influential Democratic voting blocs. During a recent meeting Mr. Mamdani held with Black business leaders, they raised concerns about how plans to freeze the rent would affect the ability of Black homeowners and developers to create generational wealth.

The worry, for many landlords and developers, is Mr. Mamdani may continue to chip away at the ability to make money through property ownership.

Charles E. Phillips, the managing partner of Recognize, a private equity firm, organized the meeting. He said there was a consensus that affordability was the key issue facing the city, but there were also concerns about whether Mr. Mamdani’s policies were the right strategy to address it.

That’s because Black people “aspire to have access to the American dream” after facing many decades of obstacles, said Don Peebles, chief executive of The Peebles Corporation and a board member of the New York Real Estate Chamber, which endorsed Mr. Cuomo in the Democratic primary.

“Some Black voters will say, ‘Wait a minute, we’re finally in a position where we have some political power to change our economic plight and you want to change the rules,’” Mr. Peebles said in explaining the resistance to Mr. Mamdani among some Black residents.

Mr. Adams has fed that perception. In a recent interview with the conservative podcaster Coleman Hughes, the mayor, a landlord himself, said that Mr. Mamdani’s proposal to freeze rents for rent-stabilized units would hurt Black landlords and make it more difficult for families of color to afford upkeep expenses on their homes.

“All your wealth is being tied up and you’re being told: ‘I don’t care what goes up around you, I don’t care that that roof repair has to be done, that you have to maintain the quality of life in that apartment. You cannot raise rent,’” the mayor said.

Jumaane Williams, the public advocate and an ally of Mr. Mamdani, said he believes that Mr. Adams and Mr. Cuomo have sought to exploit Black voters’ fears of displacement to turn them against Mr. Mamdani — efforts that he characterized as a misinformation campaign.

“They have a right to have a healthy skepticism,” Mr. Williams, who is Black, said of Black voters. “If you hear somebody talking about, ‘they’re trying to take your house’ and the little bit of that thing that you’ve earned from working hard and having your grandmother work hard, then you have a right to be scared about that.”

Mr. Williams is among a flock of Black organizers and elected officials who are working to expand Mr. Mamdani’s support in Black communities.

Letitia James, a top Democrat in New York and the state’s attorney general, is also one of Mr. Mamdani’s most prominent allies. Assemblywoman Rodneyse Bichotte Hermelyn, a former Adams ally who then supported Mr. Cuomo, endorsed Mr. Mamdani after his primary win and took him on a tour of Brooklyn’s Little Haiti neighborhood.

“Once Black voters really get to know who he is, I don’t think it will take much for them to support him,” said Ms. Bichotte Hermelyn, who leads the Brooklyn Democratic Party.

Mr. Mamdani has also made efforts to forge a stronger relationship with the Rev. Al Sharpton, one of the most high-profile Black leaders in New York, as he angles for his endorsement.

L. Joy Williams, president of the NAACP New York State conference, said Mr. Mamdani’s campaign and the Black leaders who are skeptical of it should be more open to learning from one another. After meeting with Mr. Mamdani, she said she believed he is open to listening to the concerns some Black leaders might have about him and understood the role that they could play in helping him run City Hall.

“I don’t have the same fear that others have that this is going to be a train moving without our voice and without our input,” Ms. Williams said of the campaign. “Maybe because there has never been a time in this city where our voice and our input and our organizing have not been impactful.”

Leaders with the New York City chapter of the Democratic Socialists of America, whose organizing efforts helped power Mr. Mamdani’s 12-point primary win, will now focus on registering Black voters under 40. The lack of support for Mr. Mamdani among certain segments of Black voters is generational, not racial, its organizers argue.

“Even if their parents were able to work incredibly hard and claw out a middle- or upper-middle-class lifestyle for themselves, that path is not available to them in the same way,” said Grace Mausser, the group’s co-chairwoman.

Indeed, in the majority-Black areas where Mr. Mamdani’s support was strongest, voters tended to be younger — a pattern that was consistent across race and ethnicity citywide. The median age in the majority Black precincts Mr. Mamdani won was about 45 years old, 16 years younger than in those carried by Mr. Cuomo.

His campaign has also worked to engage Black voters that other Democratic campaigns often neglect, like Black Muslims and West African immigrants. Organizers with those groups said that Mr. Mamdani’s identity as an African-born Muslim helped capture the attention of those voters, who were also inspired by his message about affordability.

“The aunties are calling and saying, ‘I want to go door-knocking,’” said AjiFanta Marenah, vice president of the Muslim Democratic Club of New York, who helped organize for Mr. Mamdani. “That’s never happened before.”

Saurabh Datar contributed reporting.