People have literally begged for this process (enforcement of border laws) to be done with care and precision for decades and it's never happened. This immigration problem was like a wound that was allowed to fester, when the wound was fresh the population asked for a bandaid and the government ignored it.
So again some history of this.
The southern boarder had mexicans on it, and there were/are mexician communities that date back to before those states were part of the union. When those states joined the union they inherited, those communites and the people on the boarder traveled back and fourth.
This breaking of the law was the statue quo, people liked the cheap labor and the mexicans like the denro, alot would work send money home and travel back and fourth.
Regan fucked things up by trying to fix the problem my legitimizing the status quo, with his amnesty which basically set the president that get here and hang on long enough you too my get made legal.
Also the failed to fix the issue.
California tried in the 1990s with prop 184 and bill clinton asked the state to let the fed handle immigration issues because they are federal power and not state powers.
But back to the border.
When regan pulled that shit it enlarge the "mexican american" along the boarder so now there are ready made place mexican can hop into.
But the people crossing the boarder are from central and south america or even fucking china, this degrades the boarder hoppers quality of life.