“Much of what we feared ended up happening. I saw our manufacturers disappear,” said Mr. Barcia, who voted against both while in the House. “When Trump talked about trade, it really did resonate with working families.”

With fewer jobs with benefits in traditional industries like autos, many people are working multiple jobs just to get by, a grueling working-class calculus to stitch together enough work to pay the rent and bills. Of the five most common occupations in Bay County, only one — a registered nurse — averages more than $25,000 a year. Manufacturing does not make the top five.

“I don’t know anyone who isn’t working two or three jobs or has a side gig,” said Kim Coonan, the owner of Coonan’s Irish Hub, a neighborhood restaurant and bar down the street from the GM Powertrain plant, a backbone of the city since it began making parts for Chevrolet in 1916. “The middle class is gone.”

Recently, there has been talk of more layoffs. Most of the stores in the Bay City mall have shuttered. Downtown is dotted with empty storefronts, between restaurants and condominiums that reflect budding efforts to remake the riverfront city into a destination.

There are not a lot of Trump signs or MAGA hats visible here. Yet there is evidence of a quiet support for Mr. Trump for being willing to take on China, even if the results have been mixed. Support for labor runs so deep that what is expressed behind closed doors is often different than what is said in public, making political opinion hard to gauge. “People wear masks here,” said one business executive, who asked not to be identified by name.

One exception to this rule: the area’s farmers, who are proudly supportive of the president. “In my group of friends, I don’t know anyone who won’t support Trump,” said Brian Johnson, who this year took over the family farm in Pinconning, north of Bay City. He received $80,000 in federal compensation from lost sales in soybeans to China last year, an amount he said prevented him from a financial disaster. For now, it seems that the people who are fortunate enough to have one job — and only one job — are thinking about politics more than others.

Jeffrey Bulls works at Nexteer, a Chinese company that bought Saginaw Steering Gear, an auto supplier and a symbol of the shift toward a new global economic order. Purchased by the Chinese out of bankruptcy in 2009, it now employs about 12,000, down from 20,000 at its peak. Mr. Bulls started a podcast in his downtime, “Independent Jeff,” that focuses on issues of concern to African-American voters. “We get taken for granted too much,” Mr. Bulls said.