In “No Property in Man,” historian Sean Wilentz explains that the southern representatives to the constitutional convention were disappointed to see rather quickly that the “widely expected movement of population to favor the south and southwest never occurred, as settlement of migrants and new immigrants disproportionately favored the North.” Page 187.
In 1800, free states had 76 members of Congress, and slave states had 65. But by 1820 the margin was 122 to 90.
Southerners had hoped that the three-fifths compromise coupled with a swelling slave population would give them a slaveholding majority in the House. In that event, the Electoral College would always produce a pro-slavery president, even while slaves could not vote.
But demography is destiny. The burgeoning population of the North rapidly gave the House more free state representatives despite the three-fifths compromise.
Now again, as in first decades of the Republic, the demographic trends of the country are rapidly filling the House with members who root out and oppose racism in all its many manifestations, whether blatant or insidious.
These same trends have not yet changed the method of selecting the president. This is the reason that racially divisive candidacies for that high office are still possible.