Though union members have historically been loyal Democrats, Trump has made inroads with rank-and-file members, stoking fears that a once-stable demographic is slipping away.

"The Democratic Party in 2016 took the worker vote for granted," Robert Forrant, a labor historian, said. "They just thought it was a given that voters, that working class voters and union voters, would stay true to the Democratic Party. It doesn't work that way anymore."

While most of the major unions have endorsed Harris, the influential Teamsters and International Association of Fire Fighters haven't yet thrown their support behind a candidate. And endorsements aside, rank-and-file members are more than welcome to buck their leadership when it comes to voting.

For all the focus on wooing the working class this election, Harris and Trump presidencies would mean very different things for union members, experts told Business Insider. They agreed that a Harris-Walz administration would support organized labor far more than a Trump-Vance White House.

Experts stressed the importance of the National Labor Relations Board, the independent federal agency that oversees labor relations and protects workers' rights. Presidents get to appoint a general counsel and board members, who together decide what issues to prioritize and investigate.

"Those really swing back and forth from one administration to the next," Harry Holzer, the former chief economist at the US Department of Labor and a professor of public policy at Georgetown University, said of the appointments. "They are like the Supreme Court of labor law. Their interpretations and where they choose to do investigations — that matters a lot."

Holzer said that the Biden-Harris appointees were significantly more pro-union and willing to investigate claims of labor law violations compared to Trump's.

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"Broadly, the NLRB during Trump narrowed the scope of unions and union protections, and under Biden either those decisions were reversed and the role of unions was restored, or in some cases further expanded," Deborah Kobes, a senior fellow at Urban Institute's Center on Labor, Human Services, Population, told Business Insider.

Kobes said that Trump's appointments restricted union elections, on-site picketing, and how dues are collected. She also noted that the Biden administration increased funding for the NLRB and significantly raised the re-hiring rate for illegally fired workers.

Though Biden has a longstanding relationship with unions and the working class— he's been known as "Scranton Joe" throughout his years in the Senate and White House — Harris doesn't benefit from the same history. Still, experts said that she has a solid pro-union record and anticipate that she will enact relatively similar policies as the president.

"In the spirit of how they think about the role of the labor movement and the right to collective bargaining, there is no daylight," said Sharon Block, a board member of the NLRB under Barack Obama and current executive director at the Center for Labor and a Just Economy at Harvard Law School. Block said that Harris' decision to choose Walz, a former union member, as her running mate also signals her focus on workers' rights.

As a Senator, Harris worked to strengthen protections for workers in extreme heat and, as Vice President, briefly chaired a task force focused on worker empowerment. In her role as chair, she spearheaded an effort to loosen federal barriers to organizing, which Block said indicates that "she believes strongly in the right to collective bargaining."

Trump focuses on worker protections rhetorically — he's been saying he wants to support American labor at rallies since September — but experts are skeptical that his policies align with his words.

As president, he passed a series of executive orders that limited collective bargaining among federal workers that Biden quickly reversed, Forrant said. Several experts pointed out that neither he nor Vance support the Protecting the Right to Organize Act, a piece of legislation that is stalled in the Senate and considered the crown jewel of pro-union labor efforts.

"It really sets out its goal explicitly about being intended to expand various labor protections related to employees, rights to organize and to collectively bargain in the workplace," Kobes said. "It includes a variety of provisions that really would work towards that, whether it's prohibiting companies from holding required anti-union meetings, to establishing penalties for companies that violate worker rights."

Holzer and Forrant both said that the PRO Act is the top legislative priority for the labor movement. Harris supports the law, which is also included in the Democratic Party's platform. Beyond NLRB appointments and the PRO Act, Holzer said that the Biden-Harris administration has turned pro-union stances into legislation like the infrastructure bill.

Trump also has policies that are not explicitly related to unions but nonetheless impact members. Holzer said some of his economic policies moving forward risk eroding union power — the proposed tariffs would likely be inflationary and recessionary, and the mass deportations would generally upend the economy.

"Most economists would say the things Trump thinks are good for the union workers really are not because they're bad for the economy, bad for the labor market," Holzer told Business Insider.

The strength of organized labor ripples beyond union members as well, as Kobes said lots of evidence suggests that increasing their wages also increases non-union wages.

Overall, the experts Business Insider spoke to concluded that a Harris administration would be better for union workers, and some said that a second Trump term could be worse than a first for workers' rights.

"There were at least a few guardrails in the first Trump administration," Holzer said. "I think those would likely be gone, both on domestic policy and foreign policy."

He fears that NLRB appointments will be more "punitive" and that Trump might engage in "retribution" against the union leaders supporting Harris.

"I think we also have to remember that union members still overwhelmingly voted for President Biden and I have no reason to think that Vice President Harris won't do as well or better with union members in this election," Block said. "She is running as part of an administration that fairly calls itself the most pro-union administration in history, or at least since the Roosevelt administration."

Despite their assessments, Trump maintains a hold on some rank-and-file members for reasons both cultural and economic.

"People haven't done enough nitty-gritty polling, but my suspicion is some of it is connected to religion, to Evangelical voters who are union members and workers, but also vote with respect to cultural issues, religion, abortion, things like that," Forrant said. "I think that an element of Donald Trump's appeal also comes from the very hard line he takes on immigration."