The post-civil war history of the Democrat Party became one of oppression
All of these arguments depend on whether you are a broad or strict constructionist of the Constitution, but the latter point is powerful.
Because Lincoln feared that the only democracy in the world was at stake, President Lincoln forced statehood on the South or on the Democrat Party.
We now face a fiercely hostile political opposition that should have been dissolved. Their only policy is to get votes anyway they can. Donald Trump, being the bold, outspoken outsider, has amplified their hatred to a fine art. If you doubt that, go to California as a conservative and speak your mind, but don't use the wrong pronouns.
The post-civil war history of the Democrat Party became one of oppression. Slavery was outlawed, but each Southern state had their way of limiting the freedom of Black people. Jim Crow laws, poll taxes, de facto segregation, and outright harassment targeted both Black individuals and women who demanded their rights.
In the South during the 1950s, most voters supported the Democrat Party, contributing to the formation of the "Solid South," a voting bloc that consistently voted Democrat. When the 60s arrived, the issue of desegregation gradually drew many Southerners away from the Democrat Party.
Then Lyndon Johnson employed the artistry of pandering or paying Blacks to vote Democrat. Johnson was convinced that welfare would cause Blacks to "vote Democrat for the next 200 years." Even after trillions spent on social welfare, the Black community stayed virtually the same, behind the eight ball and Democrat.
Some would say that many Blacks advanced in our government, becoming senators and congressmen. They did. The first and second in 1870 were Republican. The first Black Democrat US congressman did not arrive until 1945. The second in 1968.