• Updated September 11, 2013, 12:52 a.m. ET

By

• TED MANN

Democratic candidates reached out across racial and ethnic boundaries in their quests to form coalitions broad enough to win the race for mayor-a sign of a decade of change in the New York City electorate and some still to come.

Early exit poll data showed Public Advocate Bill de Blasio with strong support across ethnic groups in the mayoral primary on Tuesday, with former Comptroller Bill Thompson also generating wide appeal.

Over the nearly 12 years of Mayor Michael Bloomberg's administration, the percentage of native-born white, black and Puerto Rican voters has declined, while immigrant groups have surged as a percentage of the city's population.

Those changes are reflected in the makeup of the city electorate, making broad appeal, as opposed to strength within one racial or ethnic base, increasingly vital for candidates, said John Mollenkopf, director of the Center for Urban Research at the Graduate Center of the City University of New York.

Native-born whites with native-born white parents now make up less than one-fifth of New York City's population, said Mr. Mollenkopf, whose center studied census records and voting patterns from 2000 through 2010.

In the past, with higher percentages of native-born white and black voters, a "greater degree of racial polarization" fed voter anxiety about the direction of the city's government, he said.

"That's where Mayor Koch's popularity came from, that's where the Giuliani Democrats came from, and that's where the core of Mike Bloomberg's support came from," he said, referring to former mayors Ed Koch and Rudolph Giuliani. "Now we're at a point where you can't win a general election on the basis of native whites against everybody else, because native whites just aren't enough."

"The demographics of the city are changing," said Nancy Foner, a professor of sociology at Hunter College and the Graduate Center. "It's not just that the city is heavily immigrant and more immigrants have naturalized and are starting to vote. Also, their second-generation children have grown up and are starting to vote."

Signs of that change were visible around the city Tuesday, including at P.S. 20 in Flushing, Queens, where Frances Clay has worked the polls for 20 years. There were as many Hindi and Chinese interpreters sitting around at midmorning as there were voters.

The number of Chinese-Americans voting at P.S. 20 has grown over the past 15 years, Ms. Clay said. "What's left of the white people, they still come to vote; but it's mostly Chinese now," she said. "It's like everything in America-slowly changing."

The Chinese-American vote isn't large enough to carry a citywide election, Ms. Foner said, noting that both Comptroller John Liu, who leapt from a City Council seat to that office and was running for mayor, and U.S. Rep. Grace Meng, who rose to Congress from a state Assembly seat in Flushing, Queens, had put together multiethnic voter coalitions.

"You have to create alliances to become mayor," she said. "You can't just rely on one group. How you do that is complicated, and it's become more complicated."

Within those broad census categories, individual nationalities and ethnic groups are asserting themselves to varying degrees, Ms. Foner and Mr. Mollenkopf said.

The city's largest immigrant group, Dominican-Americans, are increasingly wielding electoral clout, said State Sen. Adriano Espaillat. He noted the frequency with which he now sees Dominicans with U.S. passports re-entering the city on trips back from the Dominican Republic.

Dominicans in New York "have become U.S. citizens, and they're now voters," he said. "The same enthusiasm they have shown back home they're now showing here."

New Yorkers wait to vote in Manhattan on Tuesday.

One citywide race was breaking down along racial lines Tuesday: the competition for comptroller. Former Gov. Eliot Spitzer was far ahead among black voters and substantially among Hispanics, while Manhattan Borough President Scott Stringer led by a wide margin among white voters.

The evolving diversity of New York electoral politics may have been muted slightly over the Bloomberg years, both by his relative popularity in seeking a second term, and the large campaign expenditures he used to win and return to the mayor's office, Ms. Foner said.

"The rising numbers of West Indian, Hispanic and Asian votes are going to make a difference in the future," she said, though they will likely do so as portions of a multiethnic coalition-the kind that can bridge division across borough and neighborhood boundaries to win support through the whole city.

Mr. Espaillat had more proof of the growing political clout of his Morningside Heights neighborhood and its Dominican residents.

He spent the eve of the primary campaigning with Mr. Thompson, who has himself made much of his Caribbean heritage in campaign materials.

"A lot of attention was paid to this neighborhood," he said.

-Joe Jackson contributed to this article.