The electoral breakthrough of a radical anti-establishment party usually attracts attention, as it raises questions about the rise of political extremism and a crisis of democratic stability or legitimacy. Some radical challengers turn out to be flash-in-the-pan phenomena (for e.g. Netherlands’ Pim Fotuyn’s List), while others prove to be highly successful and sustainable in the long-run (for e.g. France’s Front National). One important determinant of radical newcomers’ political survival is the type of interaction with the mainstream parties (Downs, 2001; Eatwell and Mudde, 2004; Meguid, 2005; Bale, 2003; Art, 2007, 2012). What strategies can mainstream political parties adopt to neutralize radical challengers and drain their electoral support? What strategies can radical newcomers adopt to put down roots in the party system and turn their initial breakthrough into sustainable political future? Should mainstream parties forcefully challenge, ignore, or, perhaps, attempt to moderate the radical newcomer? Is the radical challenger likely to benefit more from consistent combativeness with the political establishment or from moving closer to the mainstream?I argue that the effectiveness of different strategies depends on the level of popular legitimacy enjoyed by the establishment parties and on whether the radical newcomer draws its support mainly from protest voters or from ideological voters. I posit that in polities, marked by high levels of political corruption and widespread popular discontent with the functioning of the democratic regime, an accommodative strategy neutralizes and eventually hurts the political survival prospects of a radical challenger. By enticing the newcomer to support the governing coalition, the mainstream parties delegitimize the newcomer’s anti-establishment character. Sustained confrontation between the challenger and the mainstream, on the other hand, perpetuates the newcomer’s image as an outsider to a corrupt political establishment, even after the newcomer has gained parliamentary representation. This adversarial strategy thus allows the newcomer to use the benefits of parliamentary representation to build its organizational capacity, while protecting itself from potential reputational costs of looking like a sell out to a corrupt establishment. The paper illustrates these hypotheses by tracing the relationship between Bulgaria’s mainstream parties and the main radical right challenger, Ataka, since 2005.