I don’t think the Italian demographic is that large outside of the Northeast. It’s not even large enough to give Santorum a victory in NY where there is a huge Italian population.
I'm Italian. My ancestors actually came from the same area of Italy as Rick Santorum, which I only recently learned from reading Santorum’s bio.
I only recently learned the details of Santorum’s ethnic heritage because that has nothing to do with my decision to support Santorum, which was very late in the process and only after I decided he was the only choice left who (mostly) shared my values and had a realistic chance of winning.
On the other hand, a slight rephrasing of the question could change things. I do think Santorum is effectively reaching the blue collar ethnic electorate, which is often Roman Catholic and often votes Democrat. Italians are only one small part of a broader picture, but Santorum’s ethnic heritage and Catholicism gives him credibility with a demographic that is bigger than being Italian.
The old “Reagan Democrats” are not a major force anymore in national politics, but they are important in certain key states which we absolutely must win to retake the presidency this fall, and Santorum has a better shot at winning those states in the general election when most other Republicans.