This paper conducts an experimental test of the theory of ideational populism in a mostlikely case: a well-known Chilean populist presidential candidate, Roxana Miranda. At the time of our study, Chile had the necessary conditions for ideational populism: corruption scandals and a crisis of political representation that lowered citizens' trust in establishment elites. The stimulus was a speech that included the core elements of ideational populist discourse. Despite the careful experimental design and a ripe political atmosphere, we found no effects of populist discourse on voting intentions or evaluations of Miranda among the research participants. We discuss the possible reasons for these null findings. Rather than disqualifying the theory of ideational populism, we conclude that our research calls theorists to incorporate other elementsideology, gender, issue positions, strategic votinginto their models of ideational populism.For some time, the word populism has been circulating like a debased currency in the political marketplace. Politicians with a wide range of convictions and practices have strived to dissociate from the label and detach it from their actions. Scholars, conversely, have not hesitated to use it-outright and with qualifying adjectives-despite the ambiguity that surrounds it. Readers with keen eyes will notice our appropriation of the beginning lines of Schmitter and Karl's (1991) classic, "What Democracy is . . . and is not." Like democracy, populism "is a word whose meaning we must discern if it is to be of any use in guiding political analysis and practice" (Schmitter and Karl 1991: 75). The conceptual work on democracy Schmitter and Karl catalyzed has had salutary demonstration effects for scholars of populism. Indeed, lively debates have encouraged a plowing, and some winnowing, . In this same spirit, this study tests some behavioral implications of the ideational definition of populism (Hawkins and Rovira Kaltwasser forthcoming-b) with an experimental design in a most-likely case. Our results are inconsistent with predictions of the theory of ideational populism. To advance the ongoing theoretical debate, we reflect on which elements of our case might account for the slippage between expectations and empirics.We proceed as follows. First, we describe the ideational definition and theory of populism. Next we discuss former Chilean presidential candidate, Roxana Miranda, as a most-likely case for ideational populism. Then we present our experimental design. After reporting the (null) results, we conclude with reflections on what this failure can (and cannot) tell us about the validity of ideational populism.