SACRAMENTO — With proposals to bump the paychecks of working families and paeans to the legacy of the labor movement, the Democratic candidates for president are racing to line up support of influential unions in California and around the country.

The 2020 contenders are already pitching themselves as the strongest champions of workers’ rights, in hopes of winning key labor endorsements that come with armies of campaign workers. That was on display Monday night, when Sen. Kamala Harris fired up a dinner crowd at a labor conference in Sacramento, receiving multiple standing ovations.

“Unions built the middle class in this country,” Harris told about 600 cheering union members and supporters in a downtown hotel ballroom. “People have a five-day workweek because of unions. People have sick leave because of unions. People have an eight-hour workday because of unions. People have health care because of unions.”

On the same day, eight other presidential candidates addressed a union town hall event in Washington, D.C., talking up their own policy plans and labor bona fides.

Although big labor’s power is not what it once was, the union stamp of approval could be especially important in California’s primary, which will take place in March. The Golden State is one of the most expensive places in the country in which to campaign, due to its massive size and the expensive advertising rates in major population centers, and the primary will take place on the same day as contests in almost a dozen other states. Most campaigns will be stretched thin, so the state’s 2.4 million union members would be a powerful force for any candidate.

“A union endorsement means some resources, but the most important part of it is the boots on the ground,” said Steve Smith, a spokesman for the California Labor Federation, one of the hosts of the Sacramento dinner.

California’s largest unions typically participate in the endorsement process of their national affiliates and support the presidential candidate the national union chooses, although some groups in other states have broken ranks in the past. Decisions on endorsements aren’t expected until later this year or early next year.

In 2016, most of the national unions backed Hillary Clinton in the Democratic primary — decisions that provoked some unrest from rank-and-file members who supported the more liberal Bernie Sanders. In response, several are working to make their endorsement processes more open to input from all members and involve them in the decision-making.

Many of the other top candidates in the race have strong union ties, including Sen. Elizabeth Warren, Sanders and former Vice President Joe Biden, who is expected to run.

Still, Harris has the closest relationships with the California labor movement, the largest in the country by number of members. She won broad support from the state’s biggest unions during her 2016 Senate race against fellow Democrat Rep. Loretta Sanchez, getting the backing of the state Labor Federation, SEIU, Teachers Association and AFSCME branches. Laphonza Butler, the former president of SEIU California, is one of Harris’ top political strategists, and Dolores Huerta, a longtime labor leader in the state, is one of her California campaign co-chairs.

The 2020 campaign also comes at a critical moment for the labor movement, which faces increasing challenges amid declining membership rates around the country.

“Labor is not the juggernaut that it used to be,” said David McCuan, a political science professor at Sonoma State University. “Every Democratic politician still wants their endorsement and works up and down the state with them, but they just don’t have the depth of power they used to a decade ago.”

In her speech, Harris focused on two of her union-friendly policy proposals: a massive tax cut for the middle class and a plan to invest $315 billion in federal funds to give teachers around the country a raise. Some of Harris’ biggest cheers of the night came when she vowed to pay for those plans by tearing up President Trump’s tax reform bill, which cut tax rates while bestowing the largest benefits on corporations.

“On day one, we’re going to repeal that tax bill that they passed,” Harris said, arguing that it was weighed in favor of the wealthy. “They didn’t need that money. Our people need that money.”

Harris suggested that policies supporting the working class tend to get more scrutiny about how they’ll be paid for than policies helping the rich.

“These people talking about ‘how you’re going to pay for it,’ right? It’s funny how they bring up that conversation when you’re talking about figuring out how public policy can support working people,” she said.

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“She’s not afraid to call Trump out,” said Larry Yee, the secretary of Communication Workers of America Local 9410 in San Francisco. In 2016, he said, “we gave Bernie a chance,” but Sanders doesn’t have a lock on the union’s support this time.

Mel Breshears, the business manager of the AWIU 16 asbestos workers union in Benicia, said he was open-minded about the candidates and hoped to support “somebody who can go up and withstand the lies and bullsh** Trump is going to throw at them.”

“We need someone who can look him in the eye and say, ‘you’re a liar,’” Breshears said. “I know Kamala can do that.”