JOHN YANG: Candidates are heading into the campaign season's closing stretch that traditionally kicks off on Labor Day.

Former President Donald Trump was off the trail today and over the weekend, but on the offensive online.

He will speak to the Fraternal Order of Police later this week.

Meanwhile, labor was the theme for Democrats with several events in blue wall states.

Vice President Kamala Harris and President Biden made their first joint campaign appearance since the convention before an organized labor audience in Pittsburgh.

Earlier, Harris also made a pitch for unions in Detroit.

KAMALA HARRIS, Vice President of the United States (D) and U.S. Presidential Candidate: Everywhere I go, I tell people, look, you may not be a union member.

You better thank a union member... (CHEERING) (APPLAUSE) KAMALA HARRIS: ... for the five-day workweek.

You better thank a union member for sick leave.

You better thank a union member for paid leave.

What we know is, when union wages go up, everybody's wages go up.

(CHEERING) (APPLAUSE) JOHN YANG: The candidates are fighting to win key Midwestern states like Michigan, where Harris was today and where Trump was just a few days ago.

Both are determined to get as much of the union vote there as they can.

But, as our economics correspondent Paul Solman reports, Trump has also shown surprising strength among some workers.

BRIAN PANNEBECKER, Retired Autoworker: I remember my mom crying for days when John F. Kennedy was assassinated.

PAUL SOLMAN: Retired United Auto Workers member Brian Pannebecker.

So yours was a Democratic family?

BRIAN PANNEBECKER: Yes, because we were always told, well, the Democrats are for the little guy, the working man.

PAUL SOLMAN: But he's an avid Donald Trump supporter now, one of many who like Trump's positions on trade, tariffs and taking on China.

BRIAN PANNEBECKER: I put 30 autoworkers into a group called Auto Workers For Trump on Facebook.

It grew organically to 3,800 people.

ANNOUNCER: Please welcome the president of the International Brotherhood of Teamsters.

PAUL SOLMAN: As for the much larger Teamsters union, its president, Sean O'Brien, actually spoke on day one of the Republican National Convention, although he didn't endorse Donald Trump.

SEAN O'BRIEN, General President, Teamsters: We all know how Washington has run.

Working people have no chance of winning this fight.

That's why I'm here today, because I refuse to keep doing the same things my predecessors did.

PAUL SOLMAN: And so the question, is the union vote, so long thought to be faithfully Democrat, swinging Republican?

Brian Pannebecker lives just outside true blue Detroit, holds his political truths to be self-evident.

BRIAN PANNEBECKER: I just believe that the Republicans now, with their lower taxes and support of family values, is better for the average working men and women of this country than the Democrat.

PAUL SOLMAN: At a Teamsters local of oil refinery workers near Detroit, we heard much of the same.

CASIMER GUZDZIOL, Member, Teamsters Local 283: Of course, we're going to try to elect somebody that's going to be more pro-oil, right?

Drill, baby, drill.

PAUL SOLMAN: Refinery worker.

Drill, baby, drill?

BILL KIRKLAND, Member, Teamsters Local 283: I am a refinery worker, yes.

I am all for keeping my job.

I'm all for America being self-sufficient on energy, our reserves being topped off to the top.

I'm all for us being independent, so yes.

PAUL SOLMAN: But more important to Bill Kirkland, cancel culture.

BILL KIRKLAND: If you don't agree with me, you're on the other side of the line, we hate your guts.

MICHELINE "MICKI" MAYNARD, Journalist and Author: The Teamsters have always been the more Republican-leaning union.

PAUL SOLMAN: Longtime Detroit journalist Micki Maynard.

MICHELINE "MICKI" MAYNARD: And it goes back to Nixon, because Nixon pardoned Jimmy Hoffa.

And the members of the Teamsters union remembered that.

PAUL SOLMAN: The Teamsters also supported Ronald Reagan and George H.W.

Bush.

And even autoworkers began defecting in Macomb County, a northern suburb of Detroit, back in 1980, the Reagan Democrats, as imports undercut the U.S. auto industry.

Brian Pannebecker lives in Macomb, blames Democrats for the decline.

BRIAN PANNEBECKER: Do you remember a presidential candidate named Ross Perot?

And he said, if we elect Bill Clinton at that time and NAFTA is signed into law, you will hear a giant sucking sound.

And that will be all of our jobs leaving and going to Mexico.

Well, in essence, that's exactly what did happen.

PAUL SOLMAN: What many blue-collar workers think today, says Micki Maynard.

MICHELINE "MICKI" MAYNARD: There is this idea that you used to be able to drive a truck or work in a car plant and you could own a home and maybe even own a vacation home and send your kids to college and have two cars and retire comfortably.

And that, today, it doesn't exist in the way that it once did.

A lot of people have to work two and even three jobs to attain the level that one parent had back in those days.

PAUL SOLMAN: As some UAW parents made it into the middle class, they moved to the suburbs to places like Macomb County, became tax-cutting Republicans.

But there's plenty of union support for the Harris/Walz ticket, which supports stronger union rights, collective bargaining and tougher enforcement of it.

Walter Robinson said his co-workers were happy that Harris and Walz visited his local.

KAMALA HARRIS: We stand for the people and we stand for the dignity of work.

PAUL SOLMAN: Do you think more people will show up and vote now because of her?

WALTER ROBINSON JR., Member, UAW Local 900: I believe so.

PAUL SOLMAN: Walter Robinson Jr., a member of the local, works as a quality control inspector at the Ford plant across the street.

WALTER ROBINSON JR.: I believe that you will get other people that might have been on the fence because they were concerned about whether President Biden Couldn't take another four years.

And I believe that they will say, well, this is a younger candidate, so let's go.

PAUL SOLMAN: Now look, plenty of Teamsters support the Democrats too.

JARED JACKSON, Teamsters Local 283: I would never vote for a Republican.

PAUL SOLMAN: In fact, even this group of refinery workers whose jobs depend on fossil fuels was split right down the middle.

And most unions support Harris-Walz wholeheartedly, like the Service Employees International, two million members, the National Education Association, three million, the AFL-CIO itself, 12.5 million.

And at the Democratic Convention, UAW President Shawn Fain made his support crystal clear.

SHAWN FAIN, President, United Auto Workers: In 2024, who will stand with the working class in our fight for justice?

Kamala Harris.

PAUL SOLMAN: OK, so what percentage of the UAW's 400,000 or so members favor Donald Trump?

BRIAN PANNEBECKER: Seventy percent.

That's conservative.

PAUL SOLMAN: Walter Robinson's guess, more like 40 percent.

Journalist Micki Maynard?

MICHELINE "MICKI" MAYNARD: I would come down somewhere in the middle.

PAUL SOLMAN: Final question about the weeks remaining until the election.

Anybody think they're going to change their mind?

MAN: No.

MAN: No.

MAN: Not with this group of people?

(LAUGHTER) PAUL SOLMAN: What do you mean?

MAN: No, we're just -- we're just -- we know what we want.

PAUL SOLMAN: I put it this way to the UAW's Walter Robinson.

Is there anything that Kamala Harris could do that would change the minds of some of the people on the line?

WALTER ROBINSON JR.: She would probably have to pull out a magic wand or something, but then they'd call her a witch.

PAUL SOLMAN: Robinson then laughed, maybe nervously.

WALTER ROBINSON JR.: That's the thing that I had to worry about doing these -- doing all these interviews is that MAGA is going to find out where I live at and they're going to be on my front lawn and mess with me.

PAUL SOLMAN: Because, as you may have noticed, these days, tribalism runs pretty deep in America.

For the "PBS News Hour," Paul Solman in and around Detroit.