First - I'm not sure there is any obligation for a party to get the approval from an artist for use in a public event. If someone can explain the exact legal implications, then I'd be interested to know. I would think that as long as the RNC or DNC (or whatever NC) pays their ASCAP and BMI fees, then the use shouldn't constitute any breach of law. My impression is that artists hear their songs being used by people who don't necessarily espouse their same political views, and get the word out to the media in order to ensure their fans don't take it as some kind of approval of that person's policies. Plus, it's free publicity.
Second - I thought long and hard about what to say about that picture in your signature. Some comments were too easy - "Nice box," for example. I could go green and offer to get those to the recycling bin for the ladies. But, I finally decided on this, and you can tell me if I am out of line. Since all of those beers suck, I might ask if they do, too?