On pages 89-90 of “How Democracies Die” Levitsky and Ziblatt describe how black turnout was 65% or higher in critical states in the old Confederacy in the 1880 election. They write that “Democrats lost power in North Carolina, Tennessee, and Virginia in the 1880s and 1890s.”
Jim Crow put an end to the threat posed to white Democrats by the black Republican vote in the south. That much is undeniable.
But the authors fail to note that the presidential selection system effectively rendered black votes in the old Confederacy meaningless after the 1876 election, which led to the end of Reconstruction. As the map below shows, in the 1880 presidential election the south was solidly held by white Democrats:
And for that matter, even in 1876 only three states in the South went Republican:
The problem then and now is that the winner-take-all allocation of electors in a state effectively ignores all votes cast for the runners-up. This is biased against black voters in the south. Under a national vote system, all their votes would matter. Under the current system, because African-Americans are concentrated regionally in the old south, their votes are effectively meaningless in the general election for president.