The article seeks to understand what is specifically modern about populists, why we have difficulty in agreeing on who and what they are, and—importantly—how we can address the formidable challenge they present to contemporary democratic politics. It does so by detailing the classical conception of the demagogue and by showing how modernity, in its liberal and counter-liberal aspects, sought to solve conclusively the problem of the demagogue. It argues that modern populists face significant obstacles to their ambitions in the form of modern constitutionalism, yet are also armed with new weapons, including new concepts or “ideologies” for manipulation (such as “the people,” nation, race and class) and new rhetorical techniques (such as propaganda that exploits modern technology and mass media).