We evaluate the empirical effectiveness of de facto versus de jure determinants of political power in the U.S. South between the end of the nineteenth and the beginning of the twentieth century. Using previously-unexploited racially-disaggregated data on voter registration in Mississippi for the years 1896 and 1899, we show that the observed pattern of black political participation is driven by de facto disfranchisement as captured by the presence of a black political majority, which negatively affects black registration. The de jure provisions introduced with the 1890 state constitution and involving literacy tests and poll taxes exert a non-robust impact. Furthermore, a difference-in-differences approach shows that the decline in aggregate turnout pre-dates the introduction of de jure restrictions and confirms a causal effect of the presence of a black political majority. De jure restrictions intensify the influence of the latter after 1890, which suggests that the main effect of the constitutional reforms may have been an institutionalization of de facto disfranchisement.