Max Miller

Brian Poindexter, until recently a little-known Democratic candidate in a solidly Republican House district, lit a Marlboro cigarette and jammed a screwdriver into the latch of a shed door he had built. He ignored his phone, which had been blowing up in recent days because of a political scandal rocking Ohio.

“It’s crazy to have him running for Congress,” said the candidate’s father, Bob Poindexter, 68, who had made bolts for a living until he retired last year. He was watching his son work. “What would be really crazy is if he won.”

That prospect is rapidly becoming less crazy, as the campaign of Representative Max Miller, Republican of Ohio, has descended into turmoil over allegations that he had physically abused his wife and young daughter.

Mr. Poindexter, who turned 47 on Tuesday, is a hard hat-wearing, union card-carrying ironworker. With fresh opportunity — given Mr. Miller’s struggles — to win over voters in a Cleveland-area district that went for President Trump by double digits, he is the type of candidate some Democrats believe can claw back working-class voters who have flocked to Mr. Trump in recent years.

This week, he has set out to test that strategy in a Republican stronghold that is suddenly seen as competitive, and that could help Democrats retake the House.

Though he launched his campaign in January, Mr. Poindexter had been largely ignored by Democratic Party leadership until last week, when the fallout from an ugly custody battle between Mr. Miller and his ex-wife, the daughter of Senator Bernie Moreno, spilled into the national news. The district, which stretches from Amish country to the suburban shores of Lake Erie, has been considered comfortably Republican for a decade.

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