Vice-President Andrew Johnson was a Southern Democrat, so say what you want about Lincoln (EDIT: and Grant/Colfax) screwing up regarding Reconstruction, I'm sure Johnson would've been infinitely worse.
Like, at least Alabama, Mississippi, South Carolina and Louisiana didn't fall to the tide of Jim Crow and the horrors of segregation, even if they did sadly suffer from lynchings every now and then (at least their perpetrators didn't walk scot-free as they often did in, say, Georgia or Florida). Had these states been taken over by the Democrats, that would've surely happened.
I wonder what would've been the effects of a so called "Solid South" on US politics. Adelbert Ames certainly wouldn't be elected president (he was first elected governor and then senator for the state of Mississippi), which would be a shame since he was a rare example of an honest politician in the middle of the general awfulness of the Gilded Age.
EDIT: Thaddeus Stevens and his Radical buddies in Congress would probably pick fights with Johnson at every opportunity. Their goals might've been noble, but boy did they love to waste time whenever they could.