Though it showed a virtual tie, the NABTU survey represented a seven-point drop for Trump from March, the first change for the president in two years, said Sean McGarvey, the union president. He attributed the change to Trump’s management of Covid-19, calling it “the greatest mistake of his presidency.”

“It’s going to be close among my members between Biden and President Trump, but there’s been dramatic change in the last six months,” McGarvey said, adding that if Trump had been more aggressive toward the coronavirus, “He’d be bulletproof. We wouldn’t even be talking about Joe Biden now.”

However, even as they praise the Democratic presidential nominee as a less-flawed candidate than Clinton, other union leaders said they fear there’s nothing they can say to the Trump supporters among their ranks to sway their opinion between now and November.

They said parts of Biden’s record, such as his past support for the North American Free Trade Agreement and the Trans-Pacific Partnership, hurt him, and that some members still look to the pre-pandemic economy under Trump as a high point.

“It doesn’t seem like there’s anybody changing their minds,” said Don Furko, president of the United Steelworkers Local 1557 in Clairton, Pennsylvania, who said the majority of his membership is backing Trump.

In northern Minnesota, local USW officials are working to educate members on steps Trump has taken to attack organized labor and encouraging them to vote for their jobs rather than on social issues like immigration, said John Arbogast, staff representative for District 11. But, he added, “you’re not going to change a Trumpster’s opinion.”

TJ Ducklo, Biden’s national press secretary, said the former vice president “sees this election as Park Avenue vs. Scranton — a choice between someone who has always stood up for working people and believes this country was built by unions, and Donald Trump, who punishes the middle class with tax cuts that only benefit him and his rich friends.”

Samantha Zager, deputy national press secretary for the Trump campaign, said, “Throughout his 50 years in politics, Biden has consistently put special interests ahead of American workers — including in his promise to shut the economy back down if he were elected — and that’s why President Trump is seeing strong support from union members.”

At a national level, most union officials have largely lined up behind Biden, appearing with him at events and acting as campaign surrogates. But they said their efforts to spread that enthusiasm have been hindered by the pandemic, which has severely limited organized labor’s in-person ground game.

With the exception of Unite Here, most unions have avoided door-knocking in an effort to prevent spreading the virus. Labor officials said some members don’t share their cell phone numbers, which is a challenge when their efforts to boost Biden have shifted to phone-banking, texting and other virtual work. So-called labor walks — organized labor’s term of art for canvassing — are largely no more.

Pat Eiding, president of the Philadelphia AFL-CIO, said trades leaders need to talk with their members more often about Biden to be effective. A refinery closed recently in the city and Trump supporters have misleadingly made some union workers believe he'll bring back the facilities, he said.

The evidence that member outreach works, he said, is the 2008 presidential election, when they spoke frequently with the rank-and-file at job sites as early as 5 a.m. and overcame prejudice in their unions against an African-American Democratic nominee.

“We said ... the man’s Black. But here's the issues: He’ll protect you and your jobs,’” he said. “And when we were able to go directly to members, instead of just being on a bully pulpit, we were able to get them to vote for Obama. And that was not an easy thing to do.”

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