There's a simple solution to the overcrowding...an impenetrable wall/fence on the border...and the whole problem disappears.
We went through this once before, Bambi-ignorance, and you said you got it, so let's try it again.
Let us suppose your impenetrable wall and let us likewise assume that while it cannot keep out either the majority of drugs or the majority of folks living here without appropriate documentation, that it can keep out those from the south.
This still leaves thousands and thousands of homeless, terrified people searching for safe haven. It is not in Mexico. It is not in Honduras. It is not in Nicaragua. It is not anywhere they could get to.
You would have them die, uncared for and unsupported.
Or, as you put it, "the whole problem disappears."
Simple.
You seem to think that the whole of Mexico, Central America, South America, Africa, Middle East, N/S/E/W Asia can all move to America for a better life, free from persecution, and a life on welfare.
They can't.
Trump is correct, there has to be an orderly immigration system, with no one entering America illegally/undocumented.
The caravaners are safe in Mexico, so that's from where they should be seeking asylum.
Mexico let them in, so they're Mexico's problem.
Mexico overrun? then that's Mexico's fault.
Mexico should set up UN refugee camps for them.
But, hang about for another year or so....Nancy and co will basically open the borders, have sanctuary cities, etc...and the real 'fun' will begin.
Australia was so overrun by boats and asylum seekers that the Leftist govt's of Rudd/Gillard/then Rudd again had them housed in resort hotels.
Free housing, $10,000 start up packs, whitegoods etc...and welfare cash for life.
The trickle became a flood.
All very nice...until 'We the People' said..."hang on a minute, where's my free home, $10,000 start up pack, and welfare cash for life?"
Gillard/Rudd drew a line in the sand, 'no more asylum seekers coming in boats will ever be settled in Australia'.
Some asylum seekers took a chance and tried it on...only to find themselves housed in shipping containers in PNG.
Some of them are still there, the housing has improved.
Open borders will work in America for a while, but eventually it will be overrun.