From his new home in Cincinnati, JD Vance would go to St. Gertrude to meet the friar.

It was a fitting place for the millennial aspiring politician, who was drawn to the Roman Catholic Church’s ancient ways. For years he had flirted with joining the church. Now he wanted to explore the desire in earnest.

St. Gertrude Church was led by the Dominican Friars from the Province of St. Joseph, part of a religious order founded in 1216. Its sanctuary smelled of incense but felt modern, its concrete walls pierced with bright stained-glass rectangles in reds and blues.

Mr. Vance would meet with Father Henry Stephan. For months, they read works of theology, mysticism, and political and moral philosophy. Sometimes they went to coffee or lunch. It was bespoke private instruction, a hallmark of Dominicans who are known for their lives of intellect and study.

Then, one summer day in 2019, Mr. Vance, then 35, returned to St. Gertrude, this time to be baptized and receive his first communion in the Dominicans’ private chapel. The friars hosted a celebratory reception for his family with doughnuts. He chose as his patron Saint Augustine, the political theologian whose fifth-century treatise “City of God” challenged Rome’s ruling class and drew Mr. Vance to the faith.

“It was the best criticism of our modern age I’d ever read,” Mr. Vance later explained in a Catholic literary journal. “A society oriented entirely towards consumption and pleasure, spurning duty and virtue.”