Supporters listen as Democratic US Senate candidate Abdul El-Sayed speaks at a rally at Wayne State University in Detroit on October 22. - Jeff Kowalsky/AFP/Getty Images

Democrats could be poised for a revival in the heartland, as furor over high costs and doubt about President Donald Trump’s willingness to change the nation’s trajectory threaten to loosen the GOP’s grip on working-class voters.

A decade after the Trump era began, when he first turned Midwestern political battlegrounds into reliably Repub...