Begin your research by looking for articles and books on your topic. Once you've found a few, check to see what resources they cite. That will often tell you what organizations conduct research on your topic. Then track down the information from those organizations or use the websites below.
"The National Annenberg Election Survey (NAES) examines a wide range of political attitudes about candidates, issues and the traits Americans want in a president. It also has a particular emphasis on the effects of media exposure through campaign commercials and news from radio, television and newspapers." From the Annenberg Public Policy Center.