Instead, he has performed will among the evangelical Christian voters.

Santorum, who has spoken spoken with a conservative voice on social issues, a man who seeks prayers as well as votes and placed a strong emphasis on family life, received another setback in the strongly-Catholic Puerto Rico primary when Mitt Romney crushed his rivals.

Romney's "Catholic-vote" advantage over Santorum is reported to be above 20 percentage points.

Searching to find out why, the only reason Santorum could pose was the religious fervour of Catholics is less uniform than the evangelicals.

"You know, I really wish I could tell you. The bottom line is that we do well among people who take their faith seriously, and as you know, just like some Protestants are not churchgoing, they are folks who identify with a particular religion but don't necessarily practice that from the standpoint of going to church and the like. And I think folks who do practice their religion more ardently, I think we do well [with them], Santorum told Sandy Rios of American Family Radio.

"Just being Catholic by no means buys you anything in the Catholic vote anymore," said Mark Gray, a researcher at Georgetown University's Center for Applied Research in the Apostolate, who specializes in American Catholics.

Only 20% of Catholics on average said it mattered "a great deal" that a candidate share their religious beliefs, compared with one-third of non-Catholics in exit polls that asked the question.

According the the Pew Research Centre, some Catholics have mistaken Santorum's rather black and white, good and evil, moralistic campaign as one conducted by a conservative Protestant.

Sources

• Huffington Post
• Richmond Times Dispatch
• Image: Huffington Post

Dr. Kenneth L. Garver was a Pittsburgh pediatrician who specialized in medical genetics. The patriarch of a large Roman Catholic family, he had treated patients considering abortion but was strongly opposed to it.

"We sat across the table and the whole evening we talked about this issue," Mr. Santorum told an anti-abortion group last October. He left, he said, convinced "that there was only one place to be, from the standpoint of science as well as from the standpoint of faith."

For Mr. Santorum, a Republican candidate for president, that conversation was an early step on a path into a deeply conservative Catholic culture that has profoundly influenced his life as a husband, father and politician. Over the past two decades, he has undergone a religious transformation that is now spurring a national conversation about faith in the public sphere.

On the campaign trail, he has attacked President Obama for "phony theology," warned of the "dangers of contraceptives" and rejected John F. Kennedy's call for strict separation of church and state. His bold expressions of faith could affect his support in this week's Super Tuesday nominating contests, possibly helping with conservative Christians, especially in the South, but scaring off voters uncomfortable mixing so much religion in politics.

Central to Mr. Santorum's spiritual life is his wife, whom he calls "the rock which I stand upon." Before marrying, the couple decided to recommit themselves to their Catholic faith — a turnabout for Karen Santorum, who had been romantically involved with a well-known abortion provider in Pittsburgh and had openly supported abortion rights, according to several people who knew her then.

Continue reading: From nominal Catholic to clarion of faith

Image: Esquire