Organized labor could potentially turn the 2020 presidential election — if only it made up its mind.

Unions are front and center this campaign season, having hosted a dozen or so forums and town hall meetings with the Democratic hopefuls. The candidates’ labor platforms, even those of moderates such as Joe Biden and Pete Buttigieg, include more proposals to strengthen workers’ ability to organize than any election cycle in recent memory. And worker strikes have nearly canceled two Democratic debates, after candidates pledged not to cross picketing workers.

Even President Trump is making a pitch to workers a central part of his reelection bid.

But one typical fixture of an election season has been largely absent: union endorsements. The major national and international unions have refrained from endorsing anyone so far, treating the political scrum with more circumspection than in previous years.

In 2015, many of the country’s largest unions, more often aligned with Democratic candidates than Republican ones, made their picks well before the primary season began.

The Service Employees International Union (about 2 million members), the American Federation of Teachers (about 1.7 million members), and American Federation of State, County and Municipal Employees (1.4 million members) all made their endorsements of Hillary Clinton by fall 2015, a year before the election. The United Food and Commercial Workers endorsed Clinton in January of the election year.

But this year, none of those big unions have endorsed a candidate yet, in part because so many drew fire from rank-and-file members who embraced Bernie Sanders last time around.

“Unions are keeping their powder dry,” said Dane Strother, a Democratic political consultant who splits his time between Washington and California. “We’ve never had a primary like this....I think everyone is trying to see how this shakes out.”

Endorsements from small unions and local chapters of the national unions have been rolling in, however, with their hands free to weigh in after the major unions saw the consequences of a top-heavy approach in 2016.

This year, Sanders, who just won the New Hampshire primary, leads the pack with more than 15 union endorsements. Nationally, he has been endorsed by the American Postal Workers Union, which has about 200,000 members, National Nurses United, which has about 150,000, the National Union of Healthcare Workers, with about 15,000, and the United Electrical, Radio and Machine Workers of America, with about 35,000 members.

He has also been endorsed by smaller groups like teachers unions in Los Angeles, the Bay Area, Nevada and Vermont, a Service Employees International Union local in New Hampshire, and a chapter of the International Brotherhood of Electrical Workers in Iowa.

Biden has been endorsed by at least seven unions, including the International Association of Fire Fighters, with 320,000 members, the Amalgamated Transit Union with about 200,000 unions, and the International Brotherhood of Electrical Workers, with about 750,000 members. And Elizabeth Warren has been endorsed by at least three unions. Buttigieg and Amy Klobuchar, who have performed well in the primaries so far, have not been endorsed by any.

In another sign of their more deliberative approach this year, unions have been doing more outreach to their members to learn about their political views, like conducting internal polls. The majority will probably line up behind whichever Democratic candidate emerges from the bruising primary season, union leaders said.

“Any one of the candidates has a better platform and record on labor issues than Donald Trump,” said Sara Nelson, the president of the Association of Flight Attendants-CWA, AFL-CIO, which has not made an endorsement in the race. “But by far and above Bernie and Elizabeth Warren provide a dramatic change to labor law that would give real people a stake in our country and our democracy and sharing in the value that we create.”

Unions have showed their influence in other ways this election cycle, through the pro-union platforms touted by most of the major candidates. For example, all the front-runners support the federal “PRO Act” legislation that just passed the House and would give workers more power during disputes at work. All the candidates also want to repeal “right to work” laws that allow workers to opt out of paying union dues. Such universal support for labor’s top legislative priorities is a big sign Democratic presidential candidates are taking workers’ issues seriously, labor advocates and union leaders said.

Picket lines became crucial stops for Democrats on the campaign trail, with candidates visiting strikes that ranged from General Motors autoworkers in Detroit to teachers in Chicago.

And the refusal by candidates to cross picket lines nearly resulted in the cancellation of two Democratic debates — first in Los Angeles, where cafeteria workers were striking for a new contract at Loyola Marymount University and then in Ohio, where candidates pledged to support workers in a dispute with debate host CNN. In both cases, the companies settled with workers days before the events as pressure escalated.

“That was very telling,” said Jamie Horwitz, a consultant to several labor unions in Washington. “Every candidate wants to be seen in the Democratic field as a friend of labor.”

For workers like Alexandria Cutler, the national attention has been eye-opening. A 23-year-old food service worker in western Pennsylvania who has been organizing with the SEIU, Cutler got the chance to host Sanders at her home and then take him to work with her — on the bus in the rain. She also participated in a roundtable discussion with Sen. Kirsten Gillibrand of New York and former congressman Beto O’Rourke of Texas when they were in the presidential race.

Still, Cutler said she is realistic about all the attention being given to workers’ issues.

“I only feel like it’s being taking more seriously, because we’re pushing the issue,” she said. SEIU’s eventual endorsement was unlikely to influence her vote, she added.

Unions are still a powerful constituency — 15-18 percent of voters in 2016 came from households with at least one union member — but questions remain about how reliably union members will turn out for a Democratic opponent in key swing states, including Michigan, Wisconsin and Pennsylvania, where Trump won by thin margins. Those states have even more union households then the general electorate.

Trump’s appeals to disaffected workers was a significant part of his success in 2016, experts say. Hillary Clinton beat Trump in union households by only nine percentage points — half of the 18-point margin Barack Obama won over Mitt Romney in 2012, according to exit poll data. That differential was enough to tip the balance in those three states, according to an analysis by Five Thirty Eight.

“White, blue-collar men are disaffected,” said Hank Sheinkopf, a veteran Democratic political consultant in New York. “And the challenge for the unions is whether they can not allow that to happen again.”

“The unions have to prove they have any juice,” he said. “They only way they can prove that is by delivering. You don’t deliver, you don’t have any juice.”

Some unions, silent on endorsements, have weighed in in other ways, like Nevada’s powerful Culinary Union, which distributed a flier to members about the candidates’ health-care plans that seemed to warn them away from Bernie Sanders and Elizabeth Warren.

The flier made waves among Sanders supporters, causing the union to defend their work with a statement saying: “It’s disappointing that Senator Sanders’ supporters have viciously attacked the Culinary Union and working families in Nevada simply because our union has provided facts on what certain healthcare proposals might do,” wrote the union’s Secretary-Treasurer Geoconda Argüello-Kline.

Peter L. Francia, a political science professor at East Carolina University and an expert on the role unions play in politics, pointed out that the president continues to pitch himself as the best answer for workers disillusioned by years of outsourcing and trade deals like NAFTA.

“The Democratic nominee is going to have to lay out a case to those workers to try to convince them that Donald Trump didn’t deliver,” Francia said. “The candidates that make a difference to that block of voters could make a huge difference in the race.”

Lee Saunders, the president of the American Federation of State, County and Municipal Employees, said he didn’t foresee Trump finding much support among his members.

“We have been hurt the last three years, broken promises,” he said. “They have had their voices stolen in states where collective bargaining doesn’t exist any more. We had the JANUS case. We have attacks on health care, we have attacks on retirement security and then the president’s budget that came out Monday just shows where his head is."

Correction: An earlier version of this story included errors in a quote from Lee Saunders, the president of the American Federation of State, County and Municipal Employees. He said “We have attacks on health care, we have attacks on retirement security,” not “We have a tax on health care, we have a tax on retirement security.” It was also updated to be more specific about Saunders’ claims about whether his members would support Trump.

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