The national leader that represents nearly 12.5 million union workers says the two dozen candidates running for president must be "unambiguously pro-worker and pro-union" to earn the organization's endorsement.

"The path to the nomination and the White House runs through the labor movement," Richard Trumka, president of the AFL-CIO, a federation of 55 national and international unions, said Wednesday via video-conference to the Iowa Federation of Labor AFL-CIO's annual convention.

Trumka said the organization is looking for someone who lives and breathes unions, puts workers first every time — not just in front of a union audience — and has "more than platitudes" on growing the labor movement.

"Tell us about your plan to make it easier to form a union, and harder to bust it," Trumka said. "Show us that unions are more than a section on your website. Or a line in your biography."

Trumka's words opened the state AFL-CIO's annual convention in Altoona in front of more than 200 union members — and before 15 Democratic presidential candidates addressed the union crowd.

Most of the candidates, vying for Iowa's more than 100,000 union-member votes, used their 10 minutes to talk about their broader vision for America, instead of providing detailed plans for workers.

► More:Recapturing the union: Democrats fight to bring back labor voters who jumped ship to Trump

The candidates with plans

U.S. Sen. Bernie Sanders of Vermont, however, rolled out what he called the "strongest pro-union platform in the history of American politics" Wednesday, promising to double union membership in four years, allowing workers to unionize with half the workforce's support, and blocking companies from federal contracts if they move operations offshore.

"For 45 years, there has been a war waged by the corporate elite against the working class of America," Sanders said.

"What we've seen is the decimation of working families all across the country, while the wealthiest people and corporations have done phenomenally well," he said.

South Bend, Indiana, Mayor Pete Buttigieg told the crowd he, too, wants to double the number of union workers in America by raising the minimum wage to $15 per hour, imposing multi-million dollar penalties for companies that interfere with union elections, and giving federal preference to employers who have unionized labor.

"I'm also going to expand who can unionize, guaranteeing bargaining rights for all American workers, whether you drive an Uber, work at a McDonald’s franchise or mop the floors at Google," Buttigieg said. "Because it's time in the 21st Century for us to acknowledge that a gig is a job and a worker is a worker, whether you call them a contractor or not."

U.S. Rep. Tim Ryan of Ohio pledged to create a chief manufacturing officer in his administration to ensure the United States is creating jobs in burgeoning industries, like electric vehicles and solar panels.

And U.S. Sen. Michael Bennet of Colorado called for expanding apprenticeship programs, the on-the-job training programs typically used by unions.

►More: Iowa caucuses: Michael Bennet wants to raise the minimum wage to $15 in parts of US, expand tax credits

Rebuilding the middle class

Most of the candidates preached the union gospel, telling union members that labor is the best way to rebuild the middle class.

U.S. Sen. Elizabeth Warren of Massachusetts, who says she has spoken at 126 town halls in 26 states since announcing her campaign for president, pledged to have union members "at the table" for big decisions at the White House. She said it's the only way the country will fix "what's broken in our economy."

"Every single time I've appeared at one of these town halls, I have uttered this sentence: Unions built America’s middle class, and unions will rebuild America’s middle class," Warren said. "I don't just say it when I show up in this room, I say it every time. Because I believe it."

The message comes as Iowa has lost 69,000 union members in the last three decades. The U.S. shed nearly 2 million members over the same time.

"I've seen my neighbors working full-time jobs and then going to my corner bodega or the shopping center and have to use food stamps, because in this country we've so stripped the dignity of labor that one job is not enough," said U.S. Sen. Cory Booker, who is from Newark, New Jersey.

Expanding health care

All presidential candidates said they supported ensuring health care for all Americans, with Warren, Sanders and others supporting universal health care called "Medicare for All." That proposal, however, concerns union members who fear the universal health care plan could eliminate hard-fought medical benefits leaders say they've negotiated over decades.

Members would be more likely to support Medicare for All proposals that allow Americans to keep their private medical insurance, leaders have told the Des Moines Register.

Former Vice President Joe Biden and Montana Gov. Steve Bullock argued Wednesday that unions' health insurance benefits should be protected.

"You've negotiated really hard for your benefits, with your union, with the employer. In my plan, you get to keep it. You don’t have to give it up," said Biden, who supports expanding the Affordable Care Act.

"You worked like hell, you gave up wages for it. And it’s better — many of them are better — than the plans that are out there now," he said.

Biden's plan would give Americans the option for a public insurance plan, or keep their employers' insurance.

Repealing Iowa's collective bargaining changes

Sanders, Biden and U.S. Sen. Amy Klobuchar of Minnesota took aim at Iowa's 2017 law that gutted protections previously afforded to most public-sector union workers, limiting their collective bargaining powers to wages. Unions previously were able to bargain for other benefits, including health insurance, holidays and overtime pay.

The law, signed former Republican Gov. Terry Branstad, was deeply controversial and sparked massive protests by labor leaders at the Iowa Capitol.

Sanders' said his new "Workplace Democracy Plan" would "essentially repeal" those changes, which drew perhaps the loudest applause of his speech.

In his opening remarks, Ken Sagar, president of Iowa AFL-CIO, said the repeal of those collective bargaining rights had a terrible impact on Iowa’s workers. He called it Branstad’s "final flipping-off of workers in Iowa" before he left to become the U.S. ambassador to China.

Klobuchar also pledged to repeal "right-to-work" laws, which in 26 states prohibits a company and a union from signing a contract that requires workers to pay union dues or fees. Iowa's "right-to-work" law was enacted in 1947.

Are ties to labor a done deal?

Several candidates spoke of their families' ties to unions, explaining how it helped give them better opportunities in life.

Former U.S. Rep. John Delaney of Maryland said his father's local union gave him a college scholarship that changed Delaney's life. Booker spoke of his grandfather, who worked building bombers during World War II in Buxton, Iowa. That union job helped lift his family out of poverty, Booker said.

But winning the labor vote isn't a given for Democrats in 2020.

President Donald Trump snagged 38.4% of the union vote in 2016, 8 percentage points higher than Republican presidential candidate Mitt Romney had in 2012, according to FiveThirtyEight, a website focused on opinion poll analysis.

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While Democratic nominee Hillary Clinton won 55.2% of labor's vote in 2016, that was 9.6 percentage points fewer than former President Barack Obama's share four years earlier.

Trumka, the national AFL-CIO president, warned that being a Democrat is not the only qualification for the organization's endorsement. "And being a Republican isn’t a disqualifier," he said.

"2020 cannot be about personality, it must be about workers," Trumka said.

Other candidates at the forum Wednesday were former HUD Secretary Julian Castro, former congressmen Beto O'Rourke and Joe Sestak, and comedian Ben Gleib. Washington Gov. Jay Inslee was previously scheduled to appear, but did not show up. He announced later Wednesday he was dropping out of the race.

New York City Mayor Bill de Blasio joined the event via video but technical issues with the audio feed, he said on Twitter, left him sounding like he was "auditioning for Alvin and the Chipmunks." His less high pitched message was later played for the union members.

Register reporter ​​​​​​Clare Ulmer contributed to this report.

Kim Norvell covers growth and development for the Register. Reach her at knorvell@dmreg.com or 515-284-8259.

Donnelle Eller covers agriculture, the environment and energy for the Register. Reach her at deller@registermedia.com or 515-284-8457.

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