If Santorum is free to say the following about Protestants, Democrats will feel free not only to attack Santorum over his religion if he's the candidate, but also Romney over his:
"[L]ook at the shape of mainline Protestantism in this country and it is in shambles, it is gone from the world of Christianity as I see it."
There is nothing qualitatively different about that statement from Christian Evangelicals' charge that Mormonism is a cult, not Christian, or some leftists' view that Mormonism is too weird to abide. At least Obama ditched Rev. Wright. But Romney is proud of his heritage, and so is Santorum pledged to defend all his beliefs in the public square.
Santorum has just played into the hands of the left and handed them a huge opening.
Thanks a lot, pal.