Rick Santorum on the campaign trail

Rick Santorum, the former two-term senator from Pennsylvania, was known during his tenure for being one of the more socially-conservative members of Congress. And while he started out the 2012 presidential campaign as a lesser-known candidate, Santorum pulled off a stunning come-from-behind victory on the January 3 Iowa caucuses. Since then, he's gained momentum -- and has become Mitt Romney's primary rival in the fight for the nomination.

Credit: AP Photo/Charlie Neibergall