I think the problem is an attribution of intent. You see "white nationalism" but:
> Making people sleep in cages
There was a spike in the number of illegal immigrants in the last few years, facilities were swamped. This was an unfortunate but temporary measure. It would be more irresponsible to just release people into the country without establishing their identity, criminal history, or a suitable guardian (for children).
> Limiting supplies / legal assistance
There are a finite resources, especially when one party sees every penny spent on immigration matters as "racist". Politicians were sounding the alarms months before this reached crisis-levels, but the other side refused to release a single penny until after it reached critical levels.
> Separating families
When an adult and a child arrive illegally with no documents you have two major facts to deal with: the adult has just broken a law, and you cannot establish familial ties. Given the extent of child trafficking, would you rather just give any adult that says "that's my child" custody, or would you rather separate the child from the adult until you can establish if that is actually a parent? You are damned either way because your critics will say you're "separating families" or "you're a pedophile helping traffic children". Personally, I would rather be told I'm splitting families than enabling child trafficking, but I could see the argument against that preference.
So at the end of the day none of these things are happening because of white nationalism. They are happening because of an inability to control illegal immigration rates, a lack of funding for facilities, materials, and legal aid; and in order to protect minors who may be trafficked.
To me, that is the real problem. One side of the media/political spectrum has decided it's white nationalism. The other sees it as something that has to be done because the alternative is worst. And to be charitable, I am sure there is a tiny fraction of a percent of a segment of the population and people involved who are white nationalists, but to think that's the motivating force is to dismiss the vast majority of people who have good intentions.
What is also exponentially annoying is that both sides have become so polarized that they will never work together on this.