This guy's trying to do something about it, but I don't know how effective it might be:
"The non-partisan, non-profit National Political "Do Not Call" Registry has been created to help citizens with the problem of unsolicited, unwanted political phone calls. Citizens can register their phone number by going to www.StopPoliticalCalls.org. There are various options for registering -- you can ask to be removed entirely from political call lists, or you can designate at what times you would like to receive calls, from which politicans or parties, etc."