I would point out that they called rascists trash rather than white trash, but perhaps the two are synonymous in the US.
More generally, those that are poor and/or unemployed can be stirred up using a scapegoat. Speaking from personal experience, working class Brits have blindly followed the claim that EU immigration was the cause of all employment problems when the recession was really to blame. This was of course the result of what the government of the day claimed and partly why Brexit is a thing. These attitudes were present long before Brexit was a thing, Brexit just so happens to be the result (so far).
Moving back in time further, there was great animosity between native inhabitants of Bristol (the same place that threw a statue in a harbour) and Welsh migrants to moved there for work post-WW2. Again, the perception was that the Bristol jobs were being taken by those that had no right to them. Now, no one looks twice if you drive an hour across the border.
Rascism in America has deep roots, so obviously the issue is much more complex and can't be explained this simply. Nonetheless, it's not hard to manipulate people against others that have look different, have different values, a different background or a different religion. It's just playing on ignorance. These days, American politicians focus anger on Mexicans and Muslims, but it's the same story playing out as before.
> These days, American politicians focus anger on Mexicans and Muslims, but it's the same story playing out as before.
And other politicians focus anger on people who have concerns about, for example, the effect of immigration on the economy at the micro level.
All of this is as you say: playing on ignorance. But I disagree that it's just that (although I doubt you intended strong emphasis on that word)...what's actually going on is a whole bunch of things, some of which humanity and science has knowledge of (but largely ignores, depending on the topic of conversation, for complicated reasons), and a whole bunch of other stuff that we do not have knowledge of.
In an abstract conversation, most everyone can agree that we have very little understanding of how humans work, but when the discussion is of a specific, object level idea, we seem to lose access to that abstract knowledge.
