Thus, though Mr. Marshall’s résumé would not state it quite this way, he is an expert in comparative calamity. And in his well-informed view, there is a very real possibility that, except for the relative refuge of Iraqi Kurdistan, Christianity may essentially cease to exist in a country to which the apostles brought the Gospel in the first century. Of the present situation, he wrote in an email, “It is the worst in modern history, and probably in history period.”

The vast tragedy of Chaldean Catholics in Iraq today stands in painful contrast to the success story of their coreligionists in the United States. First drawn by assembly-line jobs in Henry Ford’s auto factories, and after World War II compelled to leave Iraq by a succession of coups, Chaldean immigrants scaled the educational and occupational ladders into the upper middle class. By now, many of the Detroit area’s approximately 175,000 Chaldeans live in the prosperous Oakland County suburbs.

Since the recent round of persecution began in 2004, and especially after this year’s lightning advance of ISIS fighters across the Nineveh Plain, the Chaldeans here have sought to leverage their material comfort and political savvy on behalf of their endangered brethren.

Both clergy and lay leaders have met with officials in the White House, Congress and the United Nations. Congregants have donated several hundred thousand dollars for humanitarian aid. There have been prayer vigils, rallies, the announcement of scholarship funds and an “Adopt a Refugee” program.

The Chaldeans here have been pushing for practical, realistic forms of American involvement: creation of a protected zone and safe-passage corridors for Christians still in Iraq; an increased number of refugee visas and streamlined approval by State Department and Homeland Security screeners for Christians trying to reach America. Yet it seems to have taken the videos of two journalists being decapitated for much of the nation to finally heed the warning cries from places like the Mother of God Church.

“We call this a slow-motion genocide,” said Auday P. Arabo, the lay spokesman for the St. Thomas Chaldean Catholic Diocese. “It’s unfortunate people don’t feel it until it hits home. But I guess it’s human nature that you only see what’s happening in the mirror.”

Bishop Kalabat was appointed by Pope Francis to his position — making him one of two Chaldean Catholic bishops for the United States — in early May. Soon after, he traveled to Iraq to meet with Christian refugees in the Kurdish town of Ankawa. More than 10,000 of them, soon to exceed 40,000, had taken shelter in schools and churches.