Partly it's just Trump appealing to his Rust Belt supporters. They pine for a return of the well paid jobs that used to exist in the auto sector. There's less interest in the kind of jobs that manufacturing of electronics might bring. We've all seen the pictures of Chinese factories where thousands of (mostly) women in hairnets perform fiddly tasks all day long. I doubt that that is the kind of employment the average Donald supporter craves. They want a return to the 1950s when men did manly auto factory jobs and earned enough to support a middle-class family.  But those days are gone.