This study aims to explain why some anti-systemic parties come to power while others remain as permanent opposition or disappear over time. The evidence is sought from the comparative analysis of the socialist Workers’ Party of Turkey (Türkiye İşçi Partisi, 1961-1971, permanent opposition) and the pro-Islamic Welfare Party (Refah Partisi, 1983-1998, in power). In particular, the parties are compared and contrasted in terms of their organizational style, leadership structure, and linkage with the voters. The paper argues that while the TIP built a loose and vertical local organization, the RP had a strong grassroots organization cemented through Islamic ideology. Second, while the RP had an unchallenged leadership of Necmettin Erbakan, the TIP had a fragmented leadership resulting from multiple ideological conflicts which undermined the efficiency of the decision-making process and its implementation. Finally, while the TIP was a textbook example of a programmatic party under the guidance of socialist ideology, the RP heavily relied on the distribution of clientelist resources – mostly emanating from its control in the municipalities and central government – to address voters. Overall, the RP took advantage of these strategies to rapidly extend its voter base beyond core voters, particularly in metropolitan areas, while the TIP largely remained restricted to narrow constituencies.