Rick Perry’s presidential campaign released a tough new ad Thursday targeting Rick Santorum and his history of supporting earmarks in Congress. Why is Perry attacking a candidate who has been mired in single digits in Iowa despite living there for most of the past several months?

Simple, Santorum is surging. A CNN poll of registered Iowa Republicans released Wednesday puts Santorum in third place with 16 percent of the vote – his highest share yet. It’s not an outlier. In fact, data from Perry’s internal daily tracking polling shows that the Santorum surge is real and that he has the potential to continue gaining in the days before voters gather for the caucuses next Tuesday.