Social capital is often associated with desirable political and economic outcomes. This paper connects a growing literature on the "dark side" of social capital with institutional change. We examine the downfall of democracy in interwar Germany. Using new data on Nazi Party entry in a cross-section of cities, we show that dense networks of civic associations such as bowling clubs, choirs, and animal breeders went hand-in-hand with a more rapid rise of the Nazi Party. Towns with one standard deviation higher association density saw at least one-third faster entry. All types of associations – veteran associations and non-military clubs, "bridging" and "bonding" associations – positively predict NS Party entry. Party membership, in turn, predicts electoral success. These results suggest that social capital aided the rise of the Nazi movement that ultimately destroyed Germany's first democracy. We also show that the effects of social capital were more important in the starting phase of the Nazi movement, and in towns less sympathetic to its message.