Modern democrats, and Liberal independents who still cling the notion that the Democratic party is the "lesser evil", deal with the affiliation of the Democratic Party with Slavery and establishing the Jim Crow laws by insisting the two parties switched at some point in terms of which is Liberal and which is Conservative.
First of all the definition of what is Liberal or Progressive means and what Conservative means has changed. Modern American Conservatives say they believe in Small Government, but in 19th Century France the Conservatives were the Royalists. The United States Constitution was by definition a Progressive document when it was made, but today it's Progressives who want to ignore it and Paleo Conservatives who are fundamentalists about it.
And both major parties have always had different factions with not entirely compatible ideologies within them, which usually comes to the surface during the primaries as w'ere seeing now.
To suggest that Racism is inherently incompatible with Liberalism, means modern Liberals would have to renounce their intellectual descent from Enlightenment philosophers like Voltaire who were Racist and Anti-Semitic, and Sexist.
The American Democratic and Republican parties have changed a lot, but not in the basic principles, including the main things I object to about both. Both parties were Racist, and both parties still are Racist. Back in the old days that Racism manifested differently, but they've changed today to be different only in their rhetoric.
The Republican party that opposed Slavery was at the exact same time fighting Polygamy in the Mormon territories, on the grounds that "The definition of Marriage is 1 man and 1 woman". Does it sound like they've changed their view on that? BTW there often was Homophobic subtext in the anti Polygamy propaganda, I'm sure you can guess where.
The ugly fact people try to ignore is that, not all, probably not the majority when you get down to the common people, but many of the powerful influential white people leading and supporting the Abolitionist movement were no less Racist then Slave owners, maybe more Racist, they didn't want Blacks in the country period.
This includes Lincoln himself who is quoted as saying he did not believe in Racial Equality, and as saying Whites and Blacks can't co-exist together, and to have supported Colonization, that is sending all the Slaves either back to Africa, or to some Colony somewhere else like in South or Central America. Now it's claimed he had a change of heart on this very late in life after so many Blacks fought bravely for the Union during the Civil War, I would hope that's true but it doesn't change my point here, because he ardently opposed Slavery all through his life which is why the Civil War happened largely.
This goes back to to the Abolitionists among the Founding Fathers. David Barton is famous for manipulating quotes of the Founding Fathers to make them sounds more Evangelical Christian then they really were. But his Wallbuilders site also has a lot of good information documenting opposition to Slavery among the Founding Fathers. What he leaves out there is the other quotes that show those same people also did not believe it possible for Whites and Blacks to coexist.
There was also a lot of Anti-Semitic conspiracy rhetoric in the Anti-Confederacy propaganda of the Union, largely directed as Judah Phillip Benjamin. And anti Catholic bigotry too, Conspiracy Theories that the Jesuits killed Lincoln linger to this day. Back to anti-Black Racism, Civil War propaganda also expressed outrage that Southern women would let Black slaves nurse their White babies.
Yes there was also outrage against inhumane treatment of African slaves. But for many that was equivalent to outrage over mistreatment of animals.
And the same Democratic party that supported Slavery under Andrew Jackson was also just as anti Wallstreet (or the same New England elite businessmen and bankers who would become Wallstreet) as Benrie Sanders is. Jackson considered destroying the Central Bank his greatest accomplishment. And the supporters of Slavery accused the Abolitionist movement of being supported by those rich New England elites, because it was.
Things haven't really changed. The Republicans still wish African Americans weren't here, and Democrats still support Slavery. But they use the same means to achieve these different goals, a privatized Prison System, War on Drugs, draconian crime legislation and an Income Tax on hourly wages. While often the two parties rhetoric on those issues may seem different, the end result is both are equally culpable in using those same evils to oppress African Americans and other minorities.
The Republican Party's "Southern Strategy" of the 60s is what people will most often point to as where the switch happened. All that changed was which racist party the southern racists voted for. Because Southern Racists did not want Slavery anymore, they just wanted those Negros gone.
The same modern Progressives trying to make this political realignment argument praise FDR, who refused to accept Jewish refugees when Hitler only wanted to kick them out of Germany, and then rounded Japanese Americans into internment camps. Then his hand picked heir apparent Truman committed the greatest War Crime in human history, twice. Truman is known to have said some racist things.
Also the head of the KKK endorsed Hilary Clinton. David Duke is a former Klansman, he's more dangerous then the Klan because he's more eloquent at hiding the malice in what he believes. But it still annoys me that the mainstream media only talks about his endorsements of Republicans because that fits their narrative better. That the real Klan still loves the Democratss they ignore.