You really need to read up on slander law. It has almost no relevance in political advertising. And especially when you use actual photos and actual quotes - that's not even slander outside of politics.
LIBEL AND RELATED LAWSUITS AGAINST BLOGGERS
http://www.medialaw.org/Content/NavigationMenu/Member_Resources/Litigation_Resources/Materials_by_Issue/Lawsuits_Against_Bloggers/Lawsuits_Against_Bloggers.htm