I guess you don't know the entire title of that documentary movie by Dinesh D'Souza. Look at the subtitle. It's about corruption and racism in the Democratic Party going back to the time of Andrew Jackson with his racist Trail of Tears and moving forward through all the years of the racist Democratic Party pro-slavery, etc. You'd think they are not racists to hear them talk, but their current Plantation is the inner city ghettos.
I suspect the larger problem I'd have with D'Souza's work is that it's probably simplistic in the opposite direction.
There are two myths, neither of them true but propounded. The first goes like this: 'the only reason the Republicans won the White House all but once from 1968-1992 is because they became the party of the racists' and then we're quoted a shorthand of "Goldwater voted against the 1964 act, Nixon's Southern strategy, Reagan's states rights, and Bush's Willie Horton." Sounds good and has 10% of truth at most to it. The old 'the Democrats all became Republicans' myth is nonsense since in terms of national recognition only Strom Thurmond actually did. The others - Wallace, Stennis, Eastland, Long - all stayed Democrats.
The other myth is the one the Republicans try by quoting what percentage of Republicans voted for the CRA of 1964 as opposed to Democrats, completely ignoring the context of the time. Besides, in the 1960s BOTH parties covered wider swaths of the political spectrum. There were conservative Democrats and liberal Republicans and so-called moderates in both parties. What basically happened was the Democrats - concurrent with the race issue - cut themselves apart from the centrism of the country at large by instituting quotas for everything you can name, including in their selection of delegates. As the political process changed from nominations determined primarily by the party apparatus to the primary system, some of the old guard in the Democratic Party got tossed aside. McGovern ticked off so many that went running to the Republicans that it took an entire generation to recover. And the Republicans were aided in the purge by nominating a former union President (Reagan) who spoke their language combined with their abandonment of veterans/military personnel from the perspective of such things as pardoning all the draft dodgers and reducing the defense outlay. At that time, almost everyone had served at least two years in the military because of the compulsory draft.
The ultimate irony is that the very Republican base created by the Democratic purge has aged and died off while the GOP has long assumed it would always be there. The Republicans have spent the bulk of their time since 1998 flushing the party of allies not deemed conservative enough (I say 1998 because that's the year they destroyed Gingrich over the mid-terms). The military portion of the base no longer exists because Nixon did away with the draft. (This has also drastically increased defense spending because you have to be competitive with the civilian sector to get people when you're not forcing them into two years of service).
In short, the GOP of 1998-present has been a victim of its own success by confusing winning elections with endorsement of their ideas en toto. Amazingly enough, you'd think that the party as a whole would realize they're doing the exact same thing the Democrats did from 1968-1992, when they kept getting clobbered in Presidential elections. Just like the Democrats, the GOP are winning enough elections (like holding both houses and the bulk of states) that they're not taking a close enough look at their national problem.
Race had very little to do with that one way or the other. JFK calculated in the fall of 1963 that when they passed the CRA of 1964, the Democrats would lose 4-5 white votes in the South for every black one they got. But politics is more complicated than that. The so-called New South rose with governors like Terry Stanford and William Winter and - yes - Jimmy Carter.
Now, I don't dispute the notion Democrats fire off the racist accusation like Trump firing off an ignorant tweet, but I figure it's all a tactic anyway. I was sitting in a history class (the teacher was black) when each of us went up to present who we favored in the upcoming Presidential election. Two black girls sitting behind me and one was for the Republican. The other one then told her that she couldn't vote for the Republican because - and I really wish I was making this up - "he's gonna send the blacks back to Africa." I thought nothing of it. But imagine my utter shock when the girl who was told this walked up in front of the entire class and said she was for the Democrat because the Republican "is gonna send the blacks back to Africa."
My jaw dropped. So, too, did the teacher's jaw, and he was a black Democrat who had lived through the Civil Rights era. He asked her to cite a source supporting it, and she just stood there looking at her feet.
Now that story is ridiculous, right? But it's true. The problem is that we actually have people of all races and political persuasions who actually believe stuff like that. Adults who ought to know better. I've watched people make up stories whole cloth about Clinton, Bush, Obama, Romney......and then the story is told among a group of like-minded non-thinkers and it becomes 'fact.'
My point - tied to the old racist argument - folks just don't look all that deeply on the whole. People can be conned into supporting anyone if their prejudice is jiggered just right. And that's true across the board.