Santorum only got 39% of the female vote when he tried to get reelected, it seems that when voting takes place, he doesn’t do so well with females.
I was surprised to see that he badly lost the Catholic vote in 2006 as well.
I think you’d find Santorum is still not very popular with Catholics. He seems to be most popular with Evangelicals, although that’s perhaps too broad a definition. But he’s definitely not a winner among Catholics, even though he is a Catholic.