After a self-assured John F. Kennedy bested a visibly shaky Richard Nixon in their famous 1960 debates, political television, it was said, would henceforth determine elections. Today, many claim the Internet will be the latest medium to revolutionize electoral politics. Candidates invest heavily in web and email campaigns to reach prospective voters, as well as to communicate with journalists, potential donors, and political activists. Do these efforts influence voters, expand democracy, increase the coverage of political issues, or mobilize a shrinking and apathetic...