Why are some democratically elected incumbents able to use their democratic mandate to increase their powers at the expense of the legislature, the judiciary and of citizens’ rights to the point of taking over the regime? I argue that the organizational features of the ruling party play a critical role in facilitating incumbent’s aggrandizement and, as a result, contribute to democratic backsliding. In order to concentrate power gradually over several electoral cycles and through procedurally democratic means, incumbents rely on political organizations with two characteristics: mass structures that have wide coverage, and a high degree of centralization and party discipline. While all leaders who attempt incumbent takeover do not have disciplined mass organizations, those who succeed in taking over democratic institutions are likely to have them. I show using an original dataset of incumbent takeover attempts, original data about voters and legislators in Turkey, and data from a new cross-national dataset of political parties produced by V-Dem, that these organizational features of ruling parties facilitate gradual incumbent takeover. Such parties – with a mass organization and a centralized command structure – may either be inherited from past episodes of intense political conflict, or, where the incumbent represents an ideological movement, may sometimes be successfully built by incumbents just before or during the takeover attempt.