Elon Musk supports Le Pen and she’s in the Nationalist Rally party, which was started by literal SS members

And that’s just my quick googling

And the democrats were in favor of slavery by that same logic

Assuming you're American and assuming you ever cast a vote you'll have voted for the party which pushed slavery, from which the KKK was born and which pushed for segregation and the Jim Crow laws, i.e. the "democratic" party.