Nelsy Batista started her training session for two dozen potential Bernie Sanders volunteers in Oakland’s predominantly Latino Fruitvale neighborhood by explaining how this campaign is a critical moment in the nation’s history.

“Este campaña es super importante en la historia politica,” Batista said at the start of her 90-minute presentation — all in Spanish — to the supporters gathered in an insurance office that the campaign rented for the afternoon.

For the better part of a year, Sanders has focused on appealing to Latino voters who could be key to winning California and other states with similar demographics. Since May, his campaign has been organizing block by block in Latino neighborhoods such as Fruitvale, often in meetings like this.

Batista and other Sanders staffers explain how to canvass door to door, make calls from phone banks and use the campaign’s mobile app to persuade relatives and friends to support the Vermont senator. Batista’s Oakland presentation wasn’t the only one in which participants spoke in Spanish from start to finish.

Winning the Latino vote, said Rafael Návar, director of Sanders’ California operations, “is the cornerstone of our campaign.”

Polls indicate this grassroots strategy is working. A survey this month by the Public Policy Institute of California showed 38% of likely Latino Democratic voters backing Sanders in the state’s March 3 primary, compared with 25% for former Vice President Joe Biden and 15% for Massachusetts Sen. Elizabeth Warren. That contributed to a narrow overall lead for Sanders in the poll.

Sanders had similarly strong support from Latinos in a November survey by the Berkeley IGS Poll. And nearly two-thirds of Latino voters surveyed in November by the Latino Decisions polling firm expressed favorable views of Sanders, far more than for his competitors.

“We were pretty surprised at the results,” said Jacqueline Martinez Garcel, CEO of the Latino Community Foundation, which commissioned the Latino Decisions poll.

“This shows the amount of work that’s been put in from Sanders’ campaign staff,” Garcel told The Chronicle’s “It’s All Political” podcast. “They have put in an enormous amount of staff time and money in communities where Latinos make up the majority. They are doing their homework, and it shows.”

Other campaigns are reaching out to Latino voters and have opened offices in Latino neighborhoods as well. On Friday, billionaire San Francisco activist Tom Steyer held a town hall meeting with the Chicano Latino Caucus Immigrant Democratic Club in San Francisco. Former Housing and Urban Development Secretary Julián Castro — who had been the only Latino in the Democratic field — endorsed Warren after dropping out of the race and has been campaigning for her.

But none of the remaining candidates has been focusing on Latinos for as long or as intensely as Sanders. It’s an outgrowth of his 2016 campaign, when, as a senator largely unknown outside Vermont and progressive circles, he mounted a surprisingly strong challenge to Hillary Clinton in part because Latinos flocked to his candidacy.

“Bernie was from Vermont. There’s not a lot of Latinos there, and not a lot of people knew him,” said Chuck Rocha, a senior adviser on the Sanders campaign and a longtime political operative with expertise in the Latino electorate. But Rocha said he did well because voters liked his authenticity and policies aimed at the working class.

Sanders trailed Clinton by 30 percentage points among Latinos in California when he started the 2016 campaign, but closed that gap to seven points two months before the June primary, which he narrowly lost.

When Sanders decided to run for the White House again, the campaign made a decision to focus on Latino voters from the start. Its first TV ad in Nevada, where roughly a third of the residents are Latino, was in Spanish. The state goes third in primary season voting, after Iowa and New Hampshire.

In California, nearly 40% of residents are Latino. Sanders has opened 16 offices in the state, many in predominantly Latino neighborhoods in East Los Angeles, Oxnard, the Central Valley and the Inland Empire. Last week, at a bilingual news conference at its Mission District office, the Sanders campaign announced that he had won the endorsement of the San Francisco Latino Democratic Club.

“When I show up at the door now, there’s much more recognition of who Bernie is,” said Daniel Robelo, a Sanders campaign volunteer who lives in San Leandro. “That’s changed a lot from four years ago.”

Olga Obledo said Sanders connects with Latino voters like her because he stresses issues that resonate with working-class Americans.

“The rent is too high, you can’t buy a house, and health care is too expensive,” said Obledo, 51, who lives in San Leandro. “To me, he is the only person who has been talking about the same thing for a long time. Other politicians change their mind all the time. Bernie doesn’t.”

Persuading older Latinos to support a white Jewish guy from Brooklyn can be a hard sell, acknowledged Andrea Bocanegra, 40, of Oakland.

“I tell my parents, ‘Don’t look at the person. Look at what he’s done. Look at what he’s saying,’” Bocanegra said. “He might not look like us, but he’s with us.”

Sanders has also tried to diversify his staff after criticism that his 2016 organization looked too much like him — white and male.

Now, instead of cordoning off its 150 Latino staffers to work only with Latino voters, Latinos including Rocha and national political director Analilia Mejia hold top positions in the national campaign. In California, the state director, deputy state director, field director and student organizing manager are Latino.

“I’ve been doing this 31 years, and with most campaigns, they show up in the last two weeks” in Latino neighborhoods, Rocha said. “We went there early and stayed. And now, we’re running the most Latino campaign anybody has ever run in the history of presidential campaigns.”

Editor’s note: An earlier version of this story incorrectly reported the arrangement for the Sanders campaign’s use of office space in Oakland’s Fruitvale neighborhood for canvassing training. The campaign rented the space.

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