Did you know Rick Santorum is Catholic?

Well, a new poll says, incredibly, that most GOP voters don’t:

A new poll by the Pew Research Center asked voters what they knew of a candidate’s religion. Only about a third of Republican and Republican-leaning respondents correctly identified Santorum as Catholic. Republican white, evangelical Christians were as likely to identify Santorum as one of them as they were to identify him as Catholic (about one-third in either case).

Respondents were much more likely to know that Mitt Romney is a Mormon. About two-thirds of Republican respondents correctly identified Romney’s religion.

A significant number of evangelical Protestants do not consider Mormonism to be a Christian faith, and pollsters believe that some percentage of evangelical voters are reluctant to vote for a Mormon. The size of that factor is difficult to gauge in part because the same voters who might reject Romney because of his religion also tend to be conservatives who mistrust his ideology.