With only one day before the Democratic Nevada caucus, Hillary Clinton meets students in a job skills program called YouthBuild in Las Vegas on Friday Feb. 19, 2016. Tyrone Early on right. (Photo by Melina Mara/The Washington Post)

LAS VEGAS -- Inside a bustling Tacos El Gordo on the eve of the Nevada caucuses, civil right activist Dolores Huerta intercepted potential voters as they lined up to make their lunch orders and urged them to caucus for Hillary Clinton.

The conversations were, in part, a little political history lesson about immigration reform.

"I was reminding them -- these are young Latinos, children of immigrants -- that way back in 2007, we had a great opportunity to pass immigration reform," Huerta said. "And Hillary Clinton also co-authored that bill with Senator [Ted] Kennedy. But Bernie Sanders came out against the vote."

"He was a spoiler on the immigration bill and he’s a spoiler in this campaign," Huerta said.

Earlier in the day, Huerta published an editorial online warning: "On Immigration, Bernie Sanders is Not Who He Says He Is."

The Vermont senator's 2007 vote against the comprehensive immigration reform bill has become an increasingly loud refrain from Clinton's Latino surrogates in the week before the Nevada caucuses. Sanders explains the vote by saying he opposed guest worker provision in the legislation that was akin to "slavery."

Fearing a loss to Sanders in Nevada, Clinton and her surrogates have blasted out a warning to Latinos, urging them not to trust Sanders on immigration. But the recent arrival of this message may have come too late.

“The differences on the immigration issue and the record on Latinos is one which the campaign has been attempting to get out,” said former interior secretary Ken Salazar, who joined Huerta campaigning for Clinton on Friday. But he acknowledged: "I don’t know if it’s penetrating."

With just one day before the Nevada caucuses, time has all but run out.

Huerta, a legendary Latina labor organizer who co-founded the National Farm Workers Association with Cesar Chavez, has been among a group of Clinton surrogates who has vocally criticized Sanders for siding with Republicans during past immigration fights.

Huerta said that only recently did it become clear that the campaign would need to deploy a more aggressive stance against Sanders.

“The contest is getting fiercer,” Huerta said. “I don’t think we thought it was going to get mean."

Younger latinos in particular are unaware of Sanders's past votes against comprehensive immigration reform in 2007 or his vote for a bill protecting Minutemen Militias, who patrolled the borders to apprehend immigrants.

"I don't think they know," Huerta said. "I think it's very recent that this has come out."

At Tacos El Gordo the conversations with Huerta and Salazar occurred in Spanish, most of them briefly as people slinked off to their tables to eat quietly during their lunch breaks.

On Saturday beginning at 11:00 a.m., the campaigns of Clinton and Sanders hope they have convinced enough people in the state to take hours out of their day to show up at caucuses. It's a lot to ask of working people, many of whom are employed in hospitality jobs where a weekend caucus is no less impractical than one during the week.

"Most of the people that I have talked to are supporting Hillary," Salazar said as he folded himself into a booth. "There's lot of them who have to work during the caucus so the question is, are they really going to be able to caucus because they're going to be at work."

But the challenges in Nevada have proven similar to the ones Clinton faced in Iowa, another caucus state, Salazar said.

“It’s a tough sport just like Iowa was very tough, but Hillary pulled it out. And I think we’re going to win here,” Salazar said. "But there’s a conversation that takes place in caucus states, and I think it’s very hard."

"I would expect that if we were having a primary here in Nevada that Hillary would probably be up 70 to 30,” he added.

As Salazar chatted up the lunch crowd, his message could be crystallized in an old saying told to him often by his father: “Dime con quien andas y te diré quien eres,” which translates to “tell me who you walk with and I will tell you who you are.”

“She’s been with us and I know she’ll be with us in the future,” he said.