Primarily through racist gerrymandering, voter restriction laws, voting roll purges, and election board restructuring.

Systemic racism is still embedded in the system today (hence the reaction against what's called critical race theory), but it's more invisible. In a way, this cloak is more dangerous than the actual Jim Crow laws that everyone knew about (and that almost no white people objected to--I was there, I'm a Boomer). For example, because there is no formal segregation (there's plenty of de facto segregation of course), it might seem (to those who don't want to see the reality) that Black kids do worse in public school than do White kids because of their own fault (genetics, socialization, peer pressure, etc.). Actually Black kids entering the first grade perform as well on standardized tests as do White kids, but as both groups go through school, the disparity grows. The only rational explanation is that the system itself accounts for this difference, but most White people apparently believe that everyone has an equal opportunity, and Black students somehow squander it of t heir own volition, so there's nothing to fix.