The truth is, even if China blinked out of existence tomorrow, there just wouldn’t be a need for much of the work America lost. While low-skilled labor dominated manufacturing in decades past, automation and computers have made factory floors both tremendously productive and relatively human-free. A revitalized American manufacturing sector would raise employment, but not to the levels seen in 1979—a heyday that economists say is unlikely to be repeated.

“We couldn’t afford to do that anymore,” said Hal Sirkin, a senior partner at the Boston Consulting Group who studies manufacturing. “People think about manufacturing as back-breaking work, but it’s not that anymore. It has radically changed from a demographic perspective.”

Since candidates’ views on manufacturing seem to be stuck in the 1980s, I looked into how the status of the average factory worker has changed over the past 30 years. To do that, I used a tool developed by the University of Minnesota to analyze data from the Current Population Survey, which polls a cross-section of Americans every month about their employment.

I found three things. First, it’s much harder to get by with only a high-school degree than it used to be. In 1979, nearly three-quarters of manufacturing workers didn’t have any schooling past 12th grade. Almost a third hadn’t graduated from high school. That wouldn’t fly today. By 2014, more than half the employees in factory jobs had some amount of post-secondary schooling.

That’s good for productivity. A well-educated workforce can handle the technological demands of a modern production line and support the innovations that have effectively uncoupled industrial output from staffing levels, But it means manufacturing can no longer be a bountiful provider of entry-level jobs. Previous generations traded physical exhaustion and, occasionally, a considerable risk of injury, for a wage much higher than their education would otherwise permit; the unskilled workers of today are much more likely to go into the service sector, which pays less.

Second, Millennials are much less likely to go into manufacturing than previous generations. For years, the ages of people working in the sector largely matched those of the workforce at large: In the early 1980s, a little under half of manufacturing workers were Baby Boomers, which is about the same percentage that generation represented in the overall labor force.

But while Millennials—defined here as workers born between 1982 and 2004—made up 29 percent of the American workforce in 2014, they accounted for just 22 percent of the manufacturing sector. Those 7 percentage points might not seem like much, but look at it this way: A quarter of the young workers one would expect to see on a factory floor simply aren’t there.

The reasons for this are complicated. To be sure, a major factor is that there simply are fewer manufacturing jobs for young workers to take. And while Millennial workers typically have greater access to education—which would seem to make them more qualified for high-tech manufacturing jobs—Sirkin suspects many younger workers harbor out-of-date prejudices about factory work being all about brawn. “A lot of people are saying they don’t really want to be in manufacturing, without understanding what it is like now,” he said. “It is fundamentally people working with their brains.”