At the start of the Democratic convention, Obama and McCain were essentially tied. After Obama’s historic speech, he was up by 8 points. After 3 days of attacks at the Republican convention, they are almost back to where they started. I don’t know much about politics but there seems to be a clear correlation between conventions (media coverage) and people’s preference. 

Conventions also matter because they reveal the strategies of both sides. Republicans want the ballot question to be about personalities, not issues or the last 8 years. The democratic strategy is the exact opposite. May the best campaign win.