Rick Santorum's political good fortune in the Republican presidential primaries has come about in large part because of his appeal to evangelicals.

A Roman Catholic, he is a beneficiary of more than two decades of cooperation between conservative Protestants and Catholics who set aside theological differences for the common cause of the culture war.

Now running about even with Mitt Romney, Santorum has nearly doubled his support from white evangelical Republicans.

The high regard extends to Santorum's personal life. His seven children have been home-schooled, a practice much more common among conservative American Protestants than Catholics, who have a network of parochial schools built over centuries.

And Santorum's concerns — he opposes gay marriage and abortion, and promotes traditional roles for women — contribute to that evangelical appeal.