I've been trying to correct this misconception on the this thread. A performance license is not required for a political campaign. Since it falls under commercial use, you'll need a master use license, even if it's not aired.
I've run into this personally, for sales events. The form will ask for the square footage of venue, estimated number of attendees, etc etc. There is always a magic number which is lower than you'd think (low thousands) that says "Master Use License Required" followed by contact information.
I think I am confused because I don’t understand how a political campaign would be considered a commercial enterprise. Is this something that has been addressed in copyright court decisions?
I suppose if there was a cover fee for entrance to the rally, that this would be the functional equivalent of a commercial venture, but a free rally in an open venue would not seem to be a venture where the artist would have any control over whether their song could be played versus another artist’s song.
After reading the article it appears that the Bachmann campaign used it in a political ad. That would clearly be a no no, but I don’t see how they can control the use at an open rally.