"The story of Lawrence is a story about how real change happens in America," Warren told the crowd on a frigid morning in early February. "It’s a story about power — our power — when we fight together."
And now, roughly four and a half months into the Democratic presidential primary, the campaign staffs of Sen. Bernie Sanders, I-Vt., and former Housing and Urban Development Julián Castro have become the first in history to unionize.
These symbolic and tangible nods to working-class America and overtures to the progressive wings of the party are part of a strategy to court the union vote, which will be crucial to clinching the Democratic nomination.
Even with an established name like Biden, who secured the first major labor union endorsement of the 2020 contest from the International Association of Firefighters the morning of his Pittsburgh rally, in the race and Sanders’ emphasis on the plight of America’s middle class, a field of now over 20 candidates ensures that the fight for support from organized labor will be far more competitive this time around.
"With this many candidates running, working people can afford to be selective with our vote,” John Weber, press secretary for the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), the nation’s largest federation of unions in the United States, told ABC News. "We're looking for a candidate who understands that the single best way to make our economy fairer is by making it easier to join a union. If your first priority isn't fighting for working families, we're not interested."
And unions are making it clear they expect presidential candidates to put in the work. Earlier this week, members of the National Union of Healthcare workers protested outside a Los Angeles fundraiser for Biden, and urged the former vice president to help advocate on their behalf.
"All I can say is this: Joe said "I’m a union man," Eric Pierce, a clinician at Kaiser Permanente, told ABC News. "Mr. Vice President I’m a union man too but you know as a Union man that unions are for the communities they work in and work for—they’re not just for the membership. They’re for the community. So I ask Mr. Vice President to join us, help us advocate…"
This cycle, Democrats are competing for the union vote in a new reality – one that is shaped by a dynamic that tips in favor of union membership after 2016.
A few months after IAM publicly announced its support for Clinton, newly-minted international president Bob Martinez, now sitting at the helm of the union, attended a staff conference in San Diego in January 2016, where a local president pressed him on the endorsement process, urging for a more member-driven approach during a Q&A session.
"It was apparent to me from the beginning that, you know, this is something that we should have been doing for a long time, the membership deserves the right to voice their opinion in the endorsement process," Martinez told ABC News in an interview Thursday.
"We set up a process for them to do just that," he added.
In a stark contrast from the closed-door meetings typical of Washington, the new process, unveiled this week at a legislative conference in Washington, downsizes the influence of the union’s top brass and shifts it to the organization’s members, who will be able to vote online for their candidate of choice.
Martinez said the changes seek to push the candidates to engage with the union’s rank and file through their state councils across the country, which represent the union’s political arm in each state that will ultimately vote on an endorsement. It also signals efforts to prioritize transparency and the issues most important to members, including pension reform, health care, trade, and access to unions.
"I have candidates calling me now personally, and what I'm telling them is, 'Hey, you know, you're going to have to go to the membership, you're going to have to go to our local lodges, you're going to have to go to our district meetings, you're going to have to go to our conferences, and other places where IAM members are to let them hear you. You need to, you know, ascertain their vote, face to face with them,'" Martinez said.
"I think that it's resonating well with some of the candidates, who are inquiring as to where our locations of our locals and our districts are, where they can go out and meet with them, set up meetings in different states," he continued.
The change also comes as the Democratic Party looks to stem the erosion of support from union households that it saw in 2016.
While union households backed Barack Obama in 2008 and 2012 by 20 and 18 points respectively, Hillary Clinton only won them by 9 points over Donald Trump in 2016.
A significant improvement in 2020 could be a key way Democrats win back the White House in 2020, but first candidates have to make their pitch the unions themselves.
Seeking to win over a ballroom filled with IAM members this week, seven of the Democratic candidates touted similar pro-labor riffs and blended personal and policy appeals in back-to-back pitches, including New Jersey Sen. Cory Booker, former Maryland Congressman John Delaney, New York Sen. Kirsten Gillibrand, Minnesota Sen. Amy Klobuchar, Massachusetts Congressman Seth Moulton, Ohio Congressman Tim Ryan, and Sanders.
"I’m not going to sit around and beg some president or beg some leader," Ryan said to the predominantly blue-collar audience as his cadence during the emotionally rousing speech picked up. "You want me to wait. I ain’t waiting. I ain’t waiting no more…You know I’m just a kid from steel country, old high school quarterback from Northeast Ohio, Friday Night Lights. You know what — it’s about time we have a quarterback in the White House in the United States of America."
"I stand before you today as a proud, proud, proud, child of unions," Klobuchar, who was raised in a union household, asserted before the group. "I’ve got grit, and you need grit to take this guy on and you need grit to run this country, and you need grit to win this office."
"If I'm elected president, my administration will impose an immediate moratorium on any future pension cuts to multi-employer pension plans," Sanders said at the event, announcing a pledge to block cuts to promised retirement benefits if he is vaulted to the White House. "A promise made must be a promise kept."
Martinez said IAM aims to "pull the trigger" on an endorsement after Super Tuesday when the massive Democratic field will likely be winnowed down.
In the meantime, Martinez said he hopes to hear more from Biden, California Sen. Kamala Harris, former Texas Congressman Beto O’Rourke and Massachusetts Sen. Elizabeth Warren.
"Our membership wants to hear from all the candidates," Martinez said, before adding, "I think that if they want the Machinists Union endorsement, any of them that haven't spoken to the Machinists Union membership, I think they need to get on board and come out and speak to our membership."
ABC News' Molly Nagle contributed to this report.