What particularly irks Mr. Brady, though, are some of Ms. Warren’s statements about successful entrepreneurs’ not having built their businesses entirely on their own. Attacks on the country’s wealthy elite have also grated.

“When did the word millionaire or billionaire become a bad word?” he asked. “I cheer those people on because they’ve lived the American dream.”

Ms. Warren has explained for years that she, too, cheers hard-driven capitalists, but adds that as important as private enterprise is, its successes are built on governmental investments like roads, education, police officers and firefighters. And so the winners, she argues, need to share more of their haul.

To Mr. Brady, though, the comments sound like an insult. “It’s strictly the pro-business mentality that drives me to vote,” he said.