The most important factor is that the field is going to be a lot stronger. In 2012, Santorum only surged when a string of non-Mitt Romney candidates collapsed – Rep. Michele Bachman, R-Minn,; Gov. Rick Perry, R-Tex.,; Herman Cain; and Newt Gingrich. In 2016, there is going to be a significantly deeper bench of conservative candidates with strong pro-life records and the ability to talk about social issues.
Without the ability to strongly contrast himself with other candidates, Santorum will have the same problems as always – a long record of controversial statements, support for big government policies during the Bush era, and a political career that includes losing his Senate seat in the crucial swing state of Pennsylvania by 18 points in 2006. Santorum is unlikely to repeat his 2012 performance, let alone build on it.