Evan Allardyce worked as an electrician at one of the General Motors factories that once dotted Michigan’s Saginaw county and now stand as decaying markers to thousands of jobs lost to corporate agendas. He struggled to find work after the plant closures and was forced to travel across the country for contract jobs.

So Allardyce, now a leader of a Saginaw branch of the US’s largest electricians union, understands blue-collar anger over the free trade agreements that allowed car makers and other industries to move hundreds of thousands of well-paying jobs into Mexico and Canada since the 1990s. He sees how the resulting economic decline and rising poverty in the industrial heartlands helped elect Donald Trump in 2016.

What Allardyce doesn’t understand is why so many of his own members in the International Brotherhood of Electrical Workers (IBEW) still support Trump when they have not known anything but full employment and good pay that is likely to continue for years to come, thanks to booming construction work in Saginaw. For that, he says, they can thank Joe Biden’s huge spending on infrastructure.

Yet, to Allardyce’s despair, many members of his branch will again vote for Trump.

“It’s still over 50% Democrat in this local [union branch] but 20 years it was way higher than that. Something’s happened in the last little bit. There’s a lot of reasons but part of it is generational. Those of us who’ve seen the downtimes, we’ve been beaten up a little bit. But the younger generation have only seen really great work times, have only seen busy, busy work,” he said.

“Thanks to Biden that will go on for years but they don’t see that and they don’t want to hear that credit should go to Biden. I think the younger ones feel they can make a decision more outside of the box of what’s good for their pay cheque. Trump is targeting people to get them fired up about the immigration issue or whatever and it works.”

It is political lore in many parts of the US that Trump was elected eight years ago on the back of anger in Rust belt states at the impact of the North America Free Trade Agreement (Nafta) signed into law in 1993 by Bill Clinton even if it was largely negotiated by his Republican predecessors. Millions of jobs were lost in the following decades as factories moved out of the US and the car industry took advantage of cheaper labour abroad.

In 2016, Trump won support in states with a high proportion of blue-collar worker who were key to his election by railing against Nafta as “the worst trade deal ever”. General Motors shut a dozen factories around Saginaw and moved most of that work to Mexico.

Trump was back in Saginaw on Thursday because it’s a bellwether county in a battleground state, and he was pushing the same message as eight years ago.

“Americans have watched as our country has been stripped of our jobs. By the way, this state, more than any other, you lost 60% of your automobile business over the years,” he said.

“Under my plan American workers will no longer be worried about losing their jobs to foreign nations. Instead, foreign nations will be worried about losing their jobs to America. We’re bringing them all back.”

Trump made similar promises in 2016 and while he did renegotiate some of the terms of Nafta, the car factories did not return.

Carly Hammond, a Teamsters member and Saginaw organiser for the US’s largest union confederation, the AFL-CIO, spends a lot of time talking to members about how they’re going to vote and trying to steer them toward Harris. She thinks it’s a mistake to see Nafta as the original sin that drove blue-collar workers to support Trump.

There is, said Hammond, a deep disillusion with politicians rooted in years of failure to improve working people’s lives and Trump continues to garner support by marketing himself as separate from that.

“I don’t think there is an original sin. The hurt and the pain is in the repetition. It’s death by a thousand cuts. It’s the lying became so mainstream, and just the over-promising and the under-delivering became policies. What people saw in Trump, and what they still see in Trump, is a counter-influence to the over-polished politician who does nothing but lie to you and pretend to be your friend,” she said.

“It’s the Donald Trump voters in unions that I see. I think most of them are still in the same place. The trends that I see with labour people who are Trump supporters is a tendency to be very upset with the status quo, which everyone should be. People are going to stick with Trump until they see and they feel like things are getting better for them.”

Hammond, whose grandfather worked at General Motors in Saginaw while both her parents are anti-union Republicans, said many union members continue to see the Democrats as representing corporate interests over those of American workers. She identifies President Barack Obama’s bailout of the banks following the 2008 financial crash, while millions of Americans lost their homes to foreclosure, as one of the deepest wounds that soured a lot of Democratic working-class voters on the party.

“A lot of it is our own party betrayed the working class. When Barack Obama got elected in 2008 on hope and change, the first thing he did was bail out the banks which was exactly the opposite,” she said. “The legitimate concerns that a lot of Trump voters in the unions have about the Democratic party are mostly regarding who’s bought more by corporations.”

For some union members there are also more immediate concerns at work. There is strong support for Trump among members of the United Auto Workers branch who work at a Saginaw factory making vehicle steering systems who fear that the Democrats’ promotion of electric cars will put them out of work.

The impact of the blue-collar vote may not be what it was eight years ago. Trump does better with white voters who do not have a college degree, a demographic that accounts for a high proportion of union membership.

Historically, about two-thirds of union members in Michigan do not have a degree. But white people without a college degree account for a shrinking proportion of voters in the state, falling to about 55% at this year’s election.

Still, union members matter in a state like Michigan which Trump won by fewer than 11,000 votes in 2016 and then lost by a narrow margin four years later.

Union members in Teamsters for Trump T-shirts were lined up behind the former president at Thursday’s rally in Saginaw. The Teamsters, one of the US’s largest unions, has declined to endorse a candidate, a blow to Harris, after a ballot of its membership showed a clear majority backed Trump.

“My pro-worker policies are one of the major reasons why I’ve been overwhelmingly endorsed by the rank-and-file membership,” Trump told the rally.

The IBEW has endorsed Harris in part because of the huge infrastructure spending that helped bring jobs to Saginaw, including a vast semiconductor factory. Allardyce said its construction will provide work to hundred of electricians.

“I completely give the credit to the Biden administration. We could be talking about years’ worth of work here, which is an unheard of conversation to have,” he said.

It’s a message Allardyce pushes to his members at union meetings.

“The IBEW and trade unions have traditionally got on the backs of Democrats. Even from members who tell us they’re going to support them, they say: ‘But what have they done for us?’ But now we finally have an administration that’s done something for us and they’re still not happy,” he said.

Rex Christian, an IBEW official responsible for membership recruitment in Saginaw county, said Trump supporters in the union branch mostly remain unpersuaded.

“I feel like a lot of times they’re maybe embarrassed or ashamed, ashamed because they know how we feel. But you’re not going to persuade anybody if they’ve got their mind made up,” he said. “You can try to give them facts, but they don’t want to hear it.”

Hammond will vote for Harris but does not think the vice-president breaks the cycle and will struggle to win many over union members from Trump. She points to the economy, which many Americans say is their primary concern.

“You can blame Covid or external factors but inflation rose and corporations are doing better than ever. The stock prices keep growing yet people are still struggling. People see there’s still no change,” she said.

“I don’t want to make it sound like there’s no difference between the candidates because there is and I’m a Kamala Harris supporter. But Harris, as she raises more money, has walked back her promises. She didn’t put a whole lot out there to begin with but as the weeks go by the messages are getting different. The ads are changing. It’s Harris’s race to lose and, every week that goes by, Harris is going to lose more.”