WASHINGTON — United Auto Workers President Shawn Fain, speaking to a teachers union Wednesday, repeatedly bashed Republican presidential nominee Donald Trump but did not once mention the Democrats' new prospective nominee, Vice President Kamala Harris.

The union — a key group within American labor organizing, the auto industry and battleground Michigan — had featured prominently in President Joe Biden’s reelection effort, which he ended Sunday, and could play a similar role in the Harris campaign.

"What's at stake in November isn't just about November," Fain said in a speech at the 2024 American Federation of Teachers Convention in Houston, Texas. "It's going to determine whether we go forward or backward as a nation for generations to come."

"Everything is at stake," he added, addressing a crowd that is scheduled to hear a keynote address from Harris on Thursday.

Still, Fain and the UAW have held off on endorsing her. The union leader has emphasized that he wants the organization to have thorough internal discussions before reaching a decision. It's also possible that Fain, who has not shied away from bringing national attention to the UAW, is following a similar playbook as he did with the Biden campaign to win policy concessions and assurances with an eye toward the next four years.

Fain, during a Monday night television appearance on MSNBC, voiced his support and gratitude for Biden but said the union would take its time on Harris.

“We want you to have input and talk about what we're seeing, and what what we're hearing from our members and from our board. So we're not going to rush in and just throw it out there,” Fain said in an interview with MSNBC’s Jen Psaki.

“We want to have fruitful discussions when we meet, and I think it's important we do that. We owe that to them,” he added. Fain said in the MSNBC interview that he had not spoken to Harris but missed a call from her while on a flight. He also praised her past support for the UAW, including her appearance at a picket line in 2019.

Fain emerged over the last two years as a crucial supporter and surrogate for Biden on the campaign trail as the president consistently played up his support for organized labor.

However, the union took months to back Biden because it wanted to ensure the president supported a “just transition” to electric vehicles. After a historic appearance at a UAW picket line last fall during the union’s strike against the Detroit Three, UAW leaders finally endorsed Biden in January. The union’s support still came earlier than it did for him in 2020 or for previous Democratic nominees Hillary Clinton and Barack Obama.

Even though the UAW seemed almost certain to back Biden eventually, the holdout may have helped the union gain the concessions Fain was looking for and raise the organization’s influence nationally. Support for UAW jobs, notably, was a central component of a recent Biden administration grant announcement that could send $1.7 billion to General Motors Co., Stellantis NV and others to help revitalize 11 shuttered or at-risk auto manufacturing and assembly facilities.

Other major unions, throughout Biden's defunct campaign and this week with Harris, have taken a different approach on endorsements.

The AFL-CIO, the nation’s largest federation of labor unions, representing about 12.5 million members, has already registered its support for Harris, doing so on Monday. The federation includes prominent unions like the United Steelworkers, which separately affirmed their endorsement.

"Kamala Harris listens to working people, she understands their concerns, and she works hard to address those issues head-on, with real results,” USW International President David McCall said in a Monday press release. “We need to look no further than the fact that she has been instrumental in the administration developing this nation’s first real industrial policy in decades."

The Service Employees International Union, the country’s largest private sector union, representing more than 2 million members, endorsed Harris on Sunday. "The most important thing for working people right now is uniting behind Vice President Harris, the candidate who can beat Donald Trump and finish the job that we started under the Biden-Harris administration," SEIU International President April Verrett said in a Sunday statement.

She added: "Working people are clear: Vice President Harris is the leader who has their back."

Though unions have mostly lined up behind Biden and Harris in the 2024 campaign, Republicans did get surprising support from the International Brotherhood of Teamsters last week at the Republican National Convention in Milwaukee.

Sean O'Brien, general president of the union, told the crowd in Fiserv Forum that he had been invited to address the convention by Trump. O'Brien, whose union represents freight drivers and warehouse workers nationally, didn't endorse Trump but described the former president as unafraid to hear from new voices. The speech was a break from typical partisan alignment on unions, signaling Republican efforts to attract support from the world of organized labor.

Trump, however, in his own remarks at the convention, went off script to say the polarizing Fain should be "fired immediately" as head of the UAW.

Fain, even in withholding support for Harris on Wednesday, emphasized his ardent opposition to Trump.

"It's very clear. A Donald Trump White House would be a disaster for the working class," Fain said. "He represents everything that the billionaire class and the corporate class want.

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