So what went wrong with Santorum?

[All Along The Watchtower]

Insulting mainline Protestants (a majority GOP constituency, for what it's worth), plus the fact that he's a hard-liner in comparison to the Republican Party, not to mention his extreme stances on women's rights and gays, plus the fact that being a far-right religious demagogue may play well with a certain subset of the population, but it completely turns off the rest of the population and unites them against you...all of this, in addition to a horrible political/campaign operation, plus the simple fact that making Pat Buchanan (of 1992) blush by comparison with your rhetoric, in the 2010s...

All of these are reasons why Rick Santorum's candidacy was doomed. Oh, and the fact that the GOP Establishment, while they don't trust Romney, despise someone like Santorum.

[All Along The Watchtower]

Newt appeals more to the Tea Party, Rick more to the Religious Right, which have a good deal of overlap but are not the same thing.