One party believes that if you are a certain race you should vote uniformly the same way "or you ain't black". At it's core, these are people who think other races are "too stupid" to be self-sufficient and would much rather have a steady stream of dependent people to use for support

>I feel like the left has historically been simply pro immigration, and then somehow race was brought into the conversation. I won't name the party I think responsible.

Simply false. Historically, US labor unions were anti-immigration because of competition for their own members already in the country. Go look up Cesar Chavez's view on allowing more Mexicans (especially illegal aliens) in to compete against his United Farm Workers. Unions being for unlimited, uncontrolled entry from outside the US is a very recent phenomenon.

The left wasn't pro immigration back when they were the party of workers.

Democrats have better party discipline than Republicans do, but that leads to weird outcomes like the people who most distrust the police voting for the author of the crime bill. There seems to be a tacit understanding that elections are for a political machine and not an individual person, so Biden can poll poorly and would still get votes.