Bernie Sanders also lost among White Working Class voters that still were part of the Democratic Party. Check out the following from the Intelligencer article entitled, "How Bernie Lost Michigan":
https://nymag.com/intelligencer/2020/03/how-bernie-lost-michigan-to-biden.html]
But the number that leaps off the page in the exit polls is that Biden defeated Sanders among non-college-educated white voters (a.k.a. the white working class) by a 50-45 margin, which contributed to a 52-42 advantage for Biden among white voters generally. Bernie famously won the white working-class vote in Michigan over Clinton by 57-42, and won white voters by 56-42. Theres been a furious debate since then as to whether some non-college-educated whites voted for Sanders on their way right out of the Democratic Party and into Trumps GOP. Thats unclear, but these voters represented the same percentage of the 2020 primary electorate that they did in 2016, despite sharply higher turnout overall.
The swing in Michigan from a Bernie/Clinton 57-42 win among White working-class voters to the Biden/Bernie 50-45 win among White working-class voters represents an 8 point increase from Clinton to Biden along with a whipping 12 point drop from 2016 Bernie to 2020 Bernie. If it was just about losing some White working-class voters to Trump, why didn't Bernie still do better among the White working-class voters that still remained in the Democratic Party?
Here is what I think happened. Both Bernie Sanders and Donald Trump promised that if we moved away from Free Trade and toward Protectionism in the form of things like tariffs, the industry would come back to the Industrial belt. Well, Trump won, he put tariffs on China and changed NAFTA to help the car industry, and automotive jobs are still be shipped out of the U.S., and jobs in the industrial belt have not returned. I think the White working class is saying that the no longer believe in the protectionism that Bernie and Trump were selling.