One could surmise that provisions for refugees would be an exception case augmenting a more general border policy. As is the case in the EU, I believe?
The inconvenient truth is that many illegal immigrants from South America are refugees from various US-backed coups, dictatorships, and war-on-drugs fuelled drug cartels. Unfortunately they can't always claim refugee status on these grounds.
[1] https://en.wikipedia.org/wiki/Western_Hemisphere_Institute_f...