Consider this experiment. In 2004, Kim Fridkin and other researchers at Arizona State University showed people footage of the third presidential debate, the debate plus 20 minutes of post-debate commentary on NBC, the debate plus 20 minutes’ time to read commentary on CNN.com. So who won the debate, Bush or Kerry? It depended on whether you watched the news…

People watching the debate tended to think that Kerry had won, as did those who read analysis on CNN. But those who watched the NBC post-morten had the opposite impression. Fridkin et al. write:

“Our findings suggest that voters’ attitudes are influenced by the arguments presented directly by the candidates during the debate as well as by the media’s instant analyses of the candidates’ debate performances….the impact of the candidates’ messages was often altered by the media’s instant analyses.”