A growing number of countries has experienced democratic backsliding across the globe in recent years. Previous research has mostly focused on the role of either citizens or political actors in that process, waiving the potential dynamics between citizens, parties, and institutional change. In this paper, I propose a theoretical model of democratic backsliding in which citizens' growing anti-democratic attitudes first lead to an increasingly illiberal party system. Subsequently, both dropping democratic commitment of citizens and more illiberal party systems trigger a dynamic of democratic backsliding, a process in which liberal democracies come under attack. I probe this model by combining data on citizens, parties, and political systems. At the citizen level, I leverage a Bayesian dynamic latent trait model (Claassen 2018) to estimate smooth country-year panel observations based on a wide range of survey datasets from 1990 to 2015. I develop a novel index of illiberal party systems based on the V-Party dataset to measure the extent to which anti-liberal democratic orientations in parties are prevalent in national party systems. A panel analysis of the effect of changing citizens' democratic attitudes and illiberal party systems on the deterioration of liberal democratic quality in 98 countries provides evidence for the proposed three-stage model. The results suggest that dynamic between anti-democratic developments in both citizenries elicits democratic backsliding.