Santorum collected plenty of signatures from across Indiana, but fell just shy in one congressional district - he had 800 signatures from Marion County, but Marion is split between two districts, and not enough of the 800 were from the 7th district.
Almost all of Marion County is in the IN-07, but the areas in other CDs are overwhelmingly Republican (as opposed to the heavily Democrat IN-07) and thus more likely to have people who would sign ballot petitions for Santorum.
Really.
You can stand in front of Wal-Mart and get 100 signatures on almost anything.
That’s what they did in Irving when trying to collect signatures for the wet/dry petitions.