Reading, Pa. — KEITH MANDICH had been to this theater before, to see John Mellencamp.

Now Mr. Mandich, a retired steelworker, was back in downtown Reading, Pa., to see another guy he thought of as a hero for working-class America: Senator Bernie Sanders.

In his bid for the Democratic nomination, Mr. Sanders has nurtured vocal support from young, college-educated liberals. But he also has fervent support from people who remember the era of well-paying union jobs at manufacturing plants — and who are very aware of how far we are from that time.

“I just like Bernie because he’s old like me,” joked Mack Richards, 70, another retired steelworker at the Reading event.

Pennsylvania is among the five states holding a primary on Tuesday, and it has the most delegates at stake. Since neither party has locked up its nominee yet, the state’s white working-class voters have more of a voice in the primary process than they have had in years past. In 2008, they were considered Biden voters — the white working-class denizens of Scranton, Pa., and places like it — whom Joe Biden, Scranton’s own, was supposed to win over for Barack Obama.