Are these people motivated to vote for a candidate purely because they are capable of making a religious pitch? I doubt it.
Santorum had no specifics and only ran on his personality, much like Carson. Cruz suffers as well since once you get outside of the religious pitch, he has to deal with issues like his fast track vote and his immigration shenanigans.
Trying to run solely on Evangelical sensibilities might shield him from those questions in Iowa-- where everyone is stupid-- but not anywhere else.
You can't say Santorum won because Romney's a dweeb, and then that Romney's unbeatable.
Nevertheless, Santorum still couldn't sweep the South based on his Evangelical appeal, even against Newt Gingrich with his ex-wife sleaziness. Romney was inevitable because Santorum was pathetic. Once the establishment, aided and abetted by the "conservative" media, took out Newt, Romney was inevitable.
Santorum had plenty of defined positions and a well-established history as a full-spectrum conservative. Many don’t know that he has been much more aggressive on immigration issues than practically anybody, and for a long time. BUT, he was underfunded, underorganized, lacked retail charisma and Republicans hungry for a win didn’t take well to his huge defeat in Pennsylvania in 2006. Some also resented his endorsement of Arlen Specter.
While his religious credentials helped him with conservative Catholics and Evangelicals in Iowa, they would NOT have helped him if he were not a conservative besides anyway.
Neither Cruz nor Santorum ran on simply evangelical credentials. That’s more Huckabee and Robertson turf. Huck, of course, won a majority of southern states, though he is less conservative than Santorum.