With that in mind, please allow me to also be descriptive, of how things were in the Tidewater South, 40-60 years ago. I am going to write about class, and race, which the south of my time admitted[1] existed as social constructs. I hope you all appreciate that I am attempting to keep in mind EWD's "How do we tell truths that might hurt?" as well as Dr. Mike's "Regret, by definition, comes too late / Say what you mean. Bear witness. Iterate."
"Poor white" was ethnic, but not a slur. It was in fact a positive term. Poor whites were good people, who happened to not be part of one's social group because they lacked the means. Poor whites were no longer poor whites if they came into money. (I suspect JAR's family would have been poor whites under this system, not "poor white trash")
"White trash" was ethnic, and a slur, but not an ethnic slur. White trash was no better than they should have been. They were not part of one's social group because even if they had means, they lacked manners and education. Trash could easily be richer[2] than the people in one's own circle. White trash was not an ethnic slur because although they couldn't change the 'white' part, they could always change the 'trash': not everyone could afford an education, but anyone can have manners[3]. Trash who got their shit together[4] could eventually become unmarked, but because of the positive nature of "poor white" were unlikely to become the latter, even if they lacked money.
In the time and place I experienced, "poor white trash" would have been an oxymoron[5].
Now I move from factual description (not prescription) to hypothetical, attempting to apply this construct to events of our times.
What was important to white trash of the time is that even though they were on the lowest rung of the social scale, they were still "free, white, and 21" meaning that a separate social scale existed below them. If one removes 'white' from the equation, then white trash would be just trash[6]. I note that Minneapolis is well north of the Mason-Dixon line. Cops are not well paid in the US, meaning they are unlikely to be drawn from educated social classes[7]. However, even though they are in a society where respect is deeply tied to salary, they do still have people beneath them: "thugs".
[1] Marivanna asks class to name word starting with letter 'A'. Vovochka quickly raises hand, calling out "ass!" Marivanna sternly tells him "for shame, there's no such word!" Vovochka feels back pockets, thinking how odd it is that everyone has one, yet it does not have name.
[2] compare Dolphus Raymond, who uses this to his advantage. His town would not accept a rich n%%%%%-l%%%% (in modern terms, a w%%%%%?), but they would accept a trash alcoholic whose failure to segregate could be expected. If you haven't read "To Kill a Mockingbird", Calpurnia's advice on code-switching is an interesting excerpt.
[3] "my mama always said stupid is as stupid does" Not everyone sacrifices as much for their childrens' education as Mrs. Gump.
[4] and put it in a backpack.
[5] note that Dolly doesn't refer to herself as "poor white trash". She is proud to be "white trash" because she is not now, nor ever has been, a sorority bow head.
[6] See https://news.ycombinator.com/item?id=23592167 on "sin eaters." My wife watches talent shows from the States, and asks me "why do americans always have to be proud? they're always saying 'I'm proud of you'", for which I have no good answer beyond culture. Taking away someone's pride and expecting them to listen reflectively to what one has to say is unlikely to be effective.
[7] as to manners: cops here are respectful, and view their primary focus as education, not enforcement. I see that traffic cops in the RF (as they did in the USSR) even salute the people they pull over, which (if it means anything beyond hoping for cabbage) is a nice gesture. One of my favourite russian memes is a traffic cop in a Santa outfit, with the caption being "Not only do you have to pay the ticket, but you'll have to recite a poem as well."