Although the Weimar Constitution is often identified in the public memory of European constitutional law with the failure of democracy, the rise of National Socialism, and the erosion of parliamentarism, its impact on postwar German constitutional law was not merely negative and alarming. The main issue of this research is how the 1919 Constitution, despite the historical collapse of the Weimar Republic, played a role in the development of the 1949 German Basic Law and the formulation of the model of defensive democracy. The present study, using a descriptive-analytical and historical-institutional method, shows that the Basic Law reinterpreted and reconstructed the Weimar experience at three levels: textual, institutional, and judicial. At the textual level, through the integration of some Weimar articles into Article 140; at the institutional level, through the primacy of human dignity, fundamental rights, the Federal Constitutional Court, and the limitation of anti-democratic parties; and at the judicial level, through the interpretation of the free democratic order and the formulation of criteria for prohibiting or limiting anti-constitutional parties. The research findings are that Weimar was not just a memory of failure for post-war German fundamental rights, but also an institutional memory through which German democracy evolved from a merely open and defenseless democracy to a law-abiding, rights-based, and self-defending democracy. However, this article shows that defensive democracy remains compatible with constitutionalism only if it is itself subject to due process, reasoning, proportionality, and institutional constraints.