LOS ANGELES — Pete Buttigieg has risen to the top of the Democratic presidential polls in Iowa, where 90% of the population is white. But he’s lagging in California, in part because he’s having difficulty winning over Latinos and African Americans, who make up a large chunk of the Democratic electorate in the country’s biggest state.

Buttigieg is riding a mini-wave of momentum after a recent Des Moines Register/CNN poll showed him as the favorite of 25% of likely voters in the first-in-the-nation Iowa caucuses, nearly triple his showing from a September survey. In the RealClearPolitics aggregation of Iowa polls, Buttigieg now has a narrow lead on Sens. Elizabeth Warren and Bernie Sanders and former Vice President Joe Biden.

Eric Kingsley, a delegate at the California Democratic Party’s convention over the weekend in Long Beach who watched Buttigieg at an event there, said the South Bend, Ind., mayor “gives those speeches like an Aaron Sorkin character would.” It’s a common theme among Democrats who pine for a measured, moderate candidate out of Sorkin’s Clinton-era show “The West Wing” to take on President Trump.

But Buttigieg’s Iowa boomlet will be hard to carry over to more diverse states like California unless he makes more inroads with Latinos and African Americans — voters who were key in powering Barack Obama and Hillary Clinton to the Democratic nomination in the last three elections.

California donors have accounted for 22% of the $51 million that Buttigieg has raised for his 2020 run, but that hasn’t translated into support in state polls. He is running fifth in California with 7%, far behind state front-runner Biden at 24%, according to a Public Policy Institute of California survey released Monday.

Buttigieg’s problem is especially pronounced among Latinos, who account for about a fifth of California’s likely voters, according to the Public Policy Institute of California. Nearly 60% are registered Democrats.

Half of likely Latino voters have no opinion of him, a survey released last week by the Latino Decisions polling firm found. Only 1% of the 807 likely primary voters supported him, seventh among the candidates and far behind Sanders, who was first in the poll with 31%.

“In order to win and in order to deserve to win, it is so important to connect with diverse voters, in particular in California,” Buttigieg said Sunday at a forum focused on the Latino community at California State University Los Angeles.

In addition to their concerns about health care and pocketbook issues, Buttigieg said, Latino voters tell him they’re worried about “something deeper: the way that people are being treated, singled out and told they do not belong in this country. I believe that we have a crisis of belonging, fueled by this president.”

He promised to “pick up the pieces” after defeating Trump and said he would “create a sense of belonging and policy answers so that everyone in this country can thrive.”

There’s nothing wrong with that answer, Los Angeles state Sen. María Elena Durazo said after hearing him at the Los Angeles forum.

“But I think his answers are more in tune with an Iowa audience — and I don’t mean that disrespectfully,” said Durazo, a longtime Los Angeles labor leader and vice chair of the Democratic National Committee who has not endorsed a candidate.

“It’s just not strong enough, not specific enough for Latinos in California who live these attacks every day, who know the discrimination and the racism every day,” she said. “In order to get the attention of the Latino voter — when there are so many others who have good positions — you have to jump in and be much clearer.”

In contrast to Buttigieg, Durazo noted, Sanders has opened campaign offices in east Los Angeles and Fresno, both of which have large Latino populations. Buttigieg has yet to open a California office.

Plus, she said, Sanders speaks “in such a way that grabs you. He’s talking with a real strength, real confidence.”

Sanders, who is of Polish descent, told an audience at an East Los Angeles high school on Friday that like many of them, he is the child of immigrants. “And we are sick and tired of the demonization of the immigrant community,” he said.

That passion is resonating with young Latinas like Crystal Meza, a 22-year-old from East Los Angeles, who said she is trying to decide between Buttigieg and Sanders. She attended UC Berkeley for a year but had to drop out because she couldn’t afford the cost of housing and other expenses. Now she is enrolled at Cal State Los Angeles.

Meza is leaning toward Sanders because of his proposal to eliminate student loan debt by applying a tax on stock trades that the senator estimates would raise $2 trillion over a decade.

“That would help out a lot of people like me,” Meza said. Buttigieg, who owes more than $130,000 in student loans with his husband, Chasten, does not support debt elimination but believes that low-income students should be able to get a debt-free college education. He supports expanding the Pell Grant program for low-income students.

Latinos aren’t the only demographic with whom Buttigieg is struggling. Nationally, he’s polling in the single digits among African Americans, who are expected to make up one in four Democratic primary voters.

Buttigieg fired South Bend’s first African American police chief shortly after he took office in 2012, an action he admits hurt him with the city’s black community “for years.” In June, shortly after a white police officer shot an African American man in South Bend, Buttigieg took responsibility for failing to hire more black officers in a city that is one-fourth African American. “I couldn’t get it done,” he said.

In July, Buttigieg released what his campaign dubbed “The Douglass Plan,” named after abolitionist Frederick Douglass. The 18-page document contains policy prescriptions for policing, public health, education and voting rights.

“We will tear down systemic racism so that your race has no bearing on your health or your wealth or your relationship with law enforcement,” Buttigieg said Sunday in Las Vegas.

His campaign fears that Buttigieg’s sexuality — he’s openly gay — is also an issue among African Americans. A leaked internal campaign document said focus groups of black voters in South Carolina found that “being gay was a barrier for these voters, particularly the men who seemed uncomfortable even discussing it.”

Los Angeles Democratic Rep. Maxine Waters, one of the longest-serving members of the Congressional Black Caucus, has read Buttigieg’s Douglass Plan and said she liked it. And she doesn’t think his sexuality is a problem with black voters.

“He’s very clear, very articulate, fluent,” Waters, who hasn’t endorsed a candidate yet, said at the state party convention Saturday. “I think what he has to do is keep on, getting known, going into black churches, going into the black community. The black community was a long time in coming around in the issue of LGBT, but they’re there now. I think he can connect. But he’s just got to do the work.”

Buttigieg didn’t do some of the work at the convention, skipping the meeting of the African American caucus. That didn’t please caucus member Tyron Turner, 42, a delegate from Los Angeles.

But Turner was already supporting Biden. He thinks the former vice president gives Democrats a better chance at winning back onetime Obama supporters in the Rust Belt who backed Trump in 2016.

“Sometimes Democrats can overthink things,” Turner said. “Right now, I just want to win.”

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli