Nate Silver suggests that Santorum should focus less on the "small ball" of accumulating pockets of delegates and more "game-changing" moves:

For Mr. Santorum to have a shot at winning the nomination, he will need to poll at least 5 or 10 points better across the board than he has so far — and to do so consistently enough that those polls translate into votes and then delegates.
But polls usually do not shift without a reason. They change on the basis of news, and Mr. Santorum’s campaign has had trouble driving any of it.