As of November/21
Ohio is a good example because it’s a battleground state with one Senator from each party and the state went for Clinton twice, Bush twice, Obama twice, and Trump twice. Trump won Ohio by approximately 8% both times he ran and all of the previous races going back to Clinton vs. Bush have been just as close or closer. Ohio has 16 congressional districts and judging by the elections results, it would make sense if 9 were Republicans and 7 were Democrats, but 12 are Republicans and 4 are Democrats. 75% of the state isn’t Republican, but they control 75% of the state’s congressional districts and it’s obvious that the map was drawn to give the GOP the advantage they have.
Both parties do it if they can get away with it, but the GOP does it more often and they’re a lot more blatant than the Democrats.