The decline in American manufacturing is a common refrain, particularly from Donald Trump.“We don't make anything anymore,” he told Fox News, while defending his own made-in-Mexico clothing line.

Without question, manufacturing has taken a significant hit during recent decades, and further trade deals raise questions about whether new shocks could hit manufacturing.

But there is also a different way to look at the data.

Across the country, factory owners are now grappling with a new challenge: Instead of having too many workers, they may end up with too few. Despite trade competition and outsourcing, American manufacturing still needs to replace tens of thousands of retiring boomers every year. Millennials may not be that interested in taking their place. Other industries are recruiting them with similar or better pay.

For factory owners, it all adds up to stiff competition for workers——and upward pressure on wages. “ They're harder to find and they have job offers,” says Jay Dunwell, president of Wolverine Coil Spring, a family-owned firm.“ They may be coming [ into the workforce ], but they've been plucked by other industries that are also doing as well as manufacturing,” Mr. Dunwell has begun bringing high school juniors to the factory so they can get exposed to its culture.

At RoMan Manufacturing, a maker of electrical transformers and welding equipment that his father cofounded in 1980, Robert Roth keeps a close eye on the age of his nearly 200 workers. Five are retiring this year, Mr. Roth has three community-college students enrolled in a work-placement program, with a starting wage of $ 13 an hour that rises to $17 after two years.

At a worktable inside the transformer plant, young Jason Stenguist looks flustered by the copper coils he's trying to assemble and the arrival of two visitors. It's his first week on the job. Asked about his choice of career, he says at high school he considered medical school before switching to electrical engineering. “I love working with tools. I love creating,” he says.

But to win over these young workers, manufacturers have to clear another major hurdle: parents, who lived through the worst US economic downturn since the Great Depression, telling them to avoid the factory. Millennials “ remember their father and mother both were laid off, They blame it on the manufacturing recession,” says Birgit Klohs, chief executive of The Right Place, a business development agency for western Michigan.

These concerns aren't misplaced: Employment in manufacturing has fallen from 17 million in 1970 to 12 million in 2015. When the recovery began, worker shortages first appeared in the high-skilled trades. Now shortages are appearing at the mid-skill levels.

“The gap is between the jobs that take no skills and those that require a lot of skills,” says Rob Spohr, a business professor at Montcalm Community College.“ There're enough people to fill the jobs at McDonalds and other places where you don't need to have much skill. It's that gap in between, and that's where the problem is.”

Julie Parks of Grand Rapids Community College points to another key to luring Millennials into manufacturing: a work/life balance. While their parents were content to work long hours, young people value flexibility.“ Overtime is not attractive to this generation. They really want to live their lives,” she says.