WHEN the long, grim history of Christianity’s disappearance from the Middle East is written, Ted Cruz’s performance last week at a conference organized to highlight the persecution of his co-religionists will merit at most a footnote. But sometimes a footnote can help illuminate a tragedy’s unhappy whole.

For decades, the Middle East’s increasingly beleaguered Christian communities have suffered from a fatal invisibility in the Western world. And their plight has been particularly invisible in the United States, which as a majority-Christian superpower might have been expected to provide particular support.