Let's start off with some history:
1) The founder of the Democrat party, Andrew Jackson, was a slave owner who treated indigenous people horribly.
2) The Democrat party fought the Civil War to keep slavery legal.
3) The Democrats founded the KKK
4) The Democrats passed all the Jim Crow laws that persecuted Blacks
5) The Democrats stood on the doorsteps of public schools to prevent school integration
6) Lots of Democrats voted against the Civil Rights act of 1964
7) Democrats instituted the welfare state even though they were warned that the way it was set up it would destroy Black families.
8) Even as it became clear that welfare was destroying Black families the Democrats did nothing to change it
Now let's look at Democrats today:
1) Abortion is the leading cause of death for Black Americans and Black women are 3 times more likely to abort their babies than white women. Around 80% of Planned Parenthood "clinics" are in minority neighborhoods and the PP founder said that Blacks were undesirables. Yet no Democrat talks about keeping abortion legal while fixing this huge racial disparity.
2) Inner city Blacks get horrible educations due to failed public schools yet Democrats do nothing to fix the situation in Democrat run cities like Chicago. In fact Democrats say that allowing Black parents to choose their children's school is "racist". There is clear evidence that charter schools do a much better job of educating Blacks than the public schools do but Democrats are constantly trying to shut down charter schools.
3) For years thousands of Blacks are shot in Democrat run cities yet the Democrats do nothing to fix the problem. Can you imagine that the Democrat rulers of Chicago would be sitting on their hands if thousands of whites were being shot every year?
4) Any Black who dares to disagree with white Democrats is vilified. Look at how Candice Owens, Ben Carson, and Justice Thomas are treated by Democrats. If a Republican ever talked about any Black the way that Democrats talk about Blacks who aren't Democrats we'd never hear the end of it.
5) Republicans have suggested enterprise zones to bring jobs into Black neighborhoods and the Democrats have said no.
6) Democrats tend to be very paternalist in that they say that Blacks can't succeed unless white Democrats help them.
It's clear that Democrats are the racist party who view Blacks as irredeemable.