>So Joe Biden was a Democrat when the Democrats had segregationists?

There were no de jure segregationists, but even into the 90s there was a significant bloc of conservative Southern Democrats: https://en.wikipedia.org/wiki/Blue_Dog_Coalition

Remember, the "red state/blue state" thing dates from the year 2000! There are many living politicians who date from before the phase change: Hillary Clinton (in Arkansas, now a solidly Republican state) was giving speeches on how crack turns Black children into "superpredators", Joe Biden himself coauthored the 1996 crime bill, which kicked off the mass incarceration era. Bill Clinton was running campaign ads on cutting off food stamps to welfare queens and overseeing executions of criminals. It was a different era.