This paper examines a less researched aspect of East European party politics: change within ethnic parties, which are conventionally regarded as stable or intransigent political actors. The main argument of the paper is that the decreasing relevance of a bipolar model of political competition has affected the relative positioning of ethnic parties. Their programmatic outlook, role in the party system, and mobilization strategies are being mainstreamed. Ethnic parties are no longer regarded as inevitable participants in power sharing and informal elite accommodation. They are increasingly treated by voters and the party system alike as national-level parties and national-level competitors. The paper applies the concept of mainstreaming to explain the long-term evolution of the Movement for Rights and Freedoms in Bulgarian party politics as a critical case study of ethnic party repositioning from proximity to government to parliamentary opposition. It builds an argument about the MRF's continued relevance to the party system, ensuring minority representation beyond ethnicity, as a liberal-centrist party representing distinct economic interests and political orientations within the Bulgarian electorate.