Gerrymandering
Drawing boundaries of electoral districts to favor one party over another has been with us since Gov. Elbridge Gerry in 1814. A cartoonist thought the elaborately distorted district looked like a salamander and the word Gerry-mander was coined.
Modern day electoral district boundaries are too often draw to protect incumbents or disenfranchise “others”, whether those others are different ethnic groups or different parties. Gerrymandering makes it more difficult for voters to replace legislators, too many of whose districts are “safe”.
In May, the Supreme Court reminded legislators in Cooper v. Harriss, that the Equal Protection Clause of the Constitution limits the use of race in drawing electoral district boundaries. It agreed with the lower court’s rejection of two North Carolina Congressional districts. 
Voter suppression