Democracy’s transformation into mass politics has always gone hand-in-hand with new forms of political communication and media. From the early American republic to fin de siècle Europe, the expansion of suffrage created a mass voting public whose attention became the currency of politics. Unlike ancient Athenian democracy—with its lotteries and assembled citizenry—modern democracy quickly became a rowdy arena of journalists, campaign managers, and hucksters competing, often unscrupulously, for public attention. In our digital mass democracy, that rowdiness has only intensified with the explosion of competing sources of political information and appeals. Moments of mass democracy, including our own, hold out a participatory promise while presenting risks of manipulation. For one, election cycles and expanding media can generate widely available, trustworthy information that makes possible citizens’ informed debate over vital issues of public concern. Public opinion can become a body that thinks and acts—even if only slowly or, at times, reactively. Yet the media-driven election campaign can also present new opportunities for elites to employ disinformation and deception to shape public opinion. To counter these risks, …