Outsider candidates who criticize political elites have surged globally. While most studies treat anti-elite rhetoric as a “thin” ideology, I examine variation in its content. I distinguish between two types of anti-establishment appeals: valence-base appeals—highlighting the political establishment’s governance failures—and ideological appeals portraying mainstream parties as indistinguishably neoliberal or statist. I illustrate this distinction by analyzing speeches from Argentina’s 2023 presidential election. Outsider Javier Milei employed anti-establishment rhetoric more frequently than his rivals, combining both types but emphasizing pure valence critiques of the establishment over solely ideological ones. I then test the effects of these appeals on support for outsiders through a survey experiment in Argentina. I find that in contexts of poor performance and weak partisanship, valence-based anti-establishment appeals—especially those focused on corruption— boost support across the electorate, while the effect of ideological appeals depends on voters’ prior ideological leanings.