I'd like to explore this further. I really disagree with it, but it depends on how you define "working class" - economically or culturally. If by "working class" you mean people with no college education working blue-collar jobs - more of a "cultural" definition - then OK. But if you mean purely based on economic strata, I really disagree. There are millions of people across the US making $40k, $50k, $75k, etc who have student loan debt. Low-level white-collar office workers, small business employees, teachers, government employees, people who work at nonprofits, etc.
42 million people in the US have student debt. Only about 14 million are in unions. (There's probably a decent bit of overlap there too.) Why is appealing to unions considered core working-class populist messaging, while advocating for student-loan debt isn't?