Your arguments are thoughtful and I am humbled to attract the attention of one of the moderators of this site for my posts. Your response was equally voluminous so I will attempt to address all your points in my rebuttal to your arguments.
My argument is to show how Republicans, though not perfect with all their flaws that they have (as do we all), but the Democrats tend to have more negatives for Blacks from my perspective looking historically being an outsider looking at your nation as a concerned Black male.
You appear to be proving my point with my comment about the Dred Scott decision as you stated, "The Democratic party was mostly a party of White Southerns who held the POV about Black American's being 1/5 of a man which was also incorporated into the US Constitution and served their purpose to keep Black American's without freedom, subjected to white rule and slavery on farms for free labor to enrich them and their progeny for centuries to come."
I do not consider all historic white Republicans to be perfect and consider all white Democrats to be evil. There are exceptions like Ralph Nader, while he was a Democrat, he did amazing things to fight against and reform the auto industry from manufacturing rolling death traps several decades ago, and though he did not live through his presidency I feel JFK would have many great things to improve America but from what I understand his only fault was that he made too many enemies of THEM. In the same fashion Lincoln was killed, president Garfield was killed, how I suspect McKinley was killed, and absolutely how THEY wanted Andrew Jackson dead, as Woodward and Bernstein were told by Deep Throat (aka, the late W. Mark Felt), follow the money, but I digress.
Historically before the big change in the ideals within the Democratic party where they became allies with Blacks in America, I do recognize the fact that at the outset the Constitution did make America a racist institution from it's inception. However, as my second point stated Republicans voted in full agreement to abolish slavery while the Democrats were not. Even though it could not be the catalyst to form the Civil Rights movement in those earlier years, it got the ball rolling. There were those who objected to slavery in those years like the Quakers, those who helped free Blacks through the Underground Railroad and to have a "better" life in Canada among other places.
Technologically speaking at the time, the cotton gin (at least in the deep south), was an invention that kept Blacks on the plantation picking cotton and ruined the Republicans attempt at ending slavery. Before Whitney’s gin entered into widespread use, the United States produced roughly 750,000 bales of cotton, in 1830. By 1850 that amount had exploded to 2.85 million bales. This production was concentrated almost exclusively in the South, because of the weather conditions needed for the plant to grow. Faster processing of cotton with the gin meant it was profitable for landowners to establish previously-unthinkably large cotton plantations across the south. But harvesting cotton remained a very labor-intensive undertaking. Thus, bigger cotton farms meant the need for more slaves. The slave population in the United States increased nearly five-fold in the first half of the 19th Century, and by 1860, the South provided about two-thirds of the world’s cotton supply. Southern wealth had become reliant on this one crop and thus was completely dependent on slave-labor.
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http://www.civilwar.org/resources/civil-war-history-how-the.html#)
With the video clip that you shared, various things might hinder a few individuals from their right to vote such as people moving to a new location and not solidifying their ability to vote in their new location or sick in hospital perhaps which would be unfortunate statistical outliers. The way of course to correct it is to vote en masse as Roland Martin said. Even if the 100 year old Black woman was refused her right to vote, which of course is a travesty of justice, it would be corrected if dozens (preferably hundreds or thousands) were influenced to vote for her party X to counter any possible gerrymandering. But I disagree with him how the RNC has little traction with Blacks in America. I shared this link on other threads here, but besides Dr. Ben Carson, who threw his full support behind President Elect Donald J.