"We’re going to endorse our goals," Geoconda Argüello-Kline, the union’s secretary-treasurer, said at a news conference in Las Vegas. "We are not going to endorse a candidate."

She said “we respect every single political candidate right now," while singling out Biden as someone the union has known "for many years" and who has "been our friend."

For Buttigieg and Klobuchar, the non-endorsement represents an inroad to Latino voters in a state where both candidates were polling in single digits in January but are now coming off strong finishes in Iowa and New Hampshire.

The mobilization of service employees, many of them in Las Vegas, are critical to the Nevada caucuses. And the focus on Culinary’s dispute with Sanders has been watched closely ahead of voting there.

The union and its affiliates represent some 60,000 workers in the restaurant and hospitality industries in Las Vegas and Reno. It is also the largest immigrant organization in the state, with Latinos accounting for more than half of its membership, and it is a major source of voter mobilization there.

Nevada is the early voting state with the largest Latino population, 29 percent.

Bernie Sanders. | Joe Raedle/Getty Images

The refusal to endorse is a repeat of 2016, when the union decided to stay out of the bitter primary between Sanders and Hillary Clinton.

This year, the union helped drag itself into the crossfire by criticizing Medicare for All in a leaflet to members that outraged Sanders’ supporters and other progressive groups. Union leaders were “doxed” by having personal information released on social media.

The union fired back at Sanders’ supporters on Wednesday, and on Thursday, Sanders’ campaign tweeted a message of support for the group to calm tensions.

Still, tensions linger, and the union is making sure that its members know “who wants to risk the health care they have fought for and who doesn’t,” said a source familiar with the group’s thinking.

“My mentions on Twitter are completely unmanageable,” Culinary spokeswoman Bethany Khan told POLITICO after posting on Twitter that “I'm trying to do the organizing work to make sure we have a good #NVCaucus — you know the thing that Twitter activists wish they could do.”

Andres Ramirez, a Nevada-based Democratic strategist and former vice chairman of the Democratic National Committee’s Hispanic Caucus, said Thursday that Sanders’ quarrel with the union amounted to an “unforced error.”

“It’s one thing for Culinary to tell its members and distribute fliers saying, ‘Look, we don’t think this plan is good for our union.’ It’s another thing to attack them, upset them and now get them mobilized to make sure that their members don’t vote for a candidate,” he said.

He said, “When Culinary chooses to engage, they’ve proven time and time again that they can change the outcome.”

In a statement released after the Culinary announcement, Sanders addressed the issue of some of his supporters‘ behavior.

"I very much appreciate the struggle that the Culinary Union is waging to improve the lives of working families in Nevada and throughout this country, and I agree with their key goals,” he said. "Let me also address an important issue that the Culinary union has raised regarding online harassment. Harassment of all forms is unacceptable to me, and we urge supporters of all campaigns not to engage in bullying or ugly personal attacks. Our campaign is building a multigenerational, multiracial movement of love, compassion and justice. We can certainly disagree on issues, but we must do it in a respectful manner.“

Biden had once appeared the likeliest choice for Culinary, with his deep relationships in the state and an early endorsement from state Sen. Yvanna Cancela, Culinary’s former political director. But Biden’s losses in Iowa and New Hampshire were so big that union leadership was concerned about the risks of getting involved, according to three sources familiar with the union’s politics.

“If the union thought it could make a difference, it would,” said one top Democrat in the state who is not aligned with any candidate. “Bernie Sanders basically tied in Iowa, he won New Hampshire and he has momentum heading into Nevada. So there’s not much incentive for the union to get involved now.”

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The union’s top adviser, D. Taylor, helped solidify the decision not to get involved after multiple conversations with the Nevada Democratic Party’s political godfather, former Senate Majority Leader Harry Reid. Reid has warm feelings for both Biden and Warren, whose standing took a big hit after she underperformed in New Hampshire, the state that borders her home of Massachusetts.

For Sanders, the rift with Culinary could be significant. But it was not unexpected. In 2016, when Culinary did not endorse ahead of the caucuses, Sanders’ campaign was forced to apologize for campaign staffers who wore union pins to gain access to worker dining rooms on the Las Vegas Strip.

Still, Sanders remains a force in the state after winning in New Hampshire earlier this week. In addition to the legions of volunteers he carried over from 2016, he has assembled one of the year’s most robust field operation’s in Nevada.

Like Buttigieg, he is running Spanish-language ads in the state.

“They are pretty well oiled,” said one Democratic organizer in Nevada who is neutral in the contest. “They’re not running a rag-tag shop. They have all sorts of capacity.”