Welcome to all three of you. There is no cap on the amount of expenditures. Its function in the system was intended by the court to increase the number of voices that were able to participate in the process. In practice, it is able to set the agenda, that is, focus on issues that might not otherwise be the focus of the campaign, shift the balance of discourse by putting more money behind some messages than others, and when it is coherent and behind a party, create a sense on the part of the electorate of the ideological grounding of that party. Well, it depends.
Issue ads are sort of like kibitzers at a card game.
If they circle the table long enough, someone's going to start rearranging his hand. And that's what they hope to do in one way or another. You're talking tens of thousands of dollars versus tens of millions of dollars. So if they can get a media bump from them, that's a good effect for them, also, to stir up some grassroots activity. And the third thing they can try to do is make a candidate spend more money defending him or herself on a specific issue that the special interest ad raises.