The hard question that bedevils the discussion about the politics of immigration is the underlying question that no one seems to want to address.
We have a mythos here in America that we are nation of immigrants.
This is a true statement to this point.
But the immigration that made America the country that we are today was selected as a policy because of the seemingly unlimited access to resources and land that characterized a fairly empty continent awash with resources and an undamaged environment.
During the immigrant phase of the country's development, we were in a system characterized by an expanding resource base and and expanding energy base. In such a setting, immigration makes sense because it allows growth of both the productive capacity and the consumer base that is mutually dependent on it.
I would posit that those preconditions no longer exist. Oil production and exploration in the US peaked in the early 1980's. The Iron Range is mined out. We have destroyed a major chunk of the local agricultural capacity that used to feed the cities that is surrounded it and replaced it with McMansions.
We are just now getting a handle on reducing the environmental damage from the growth period characterized by the period of open immigration. It will take centuries to return it to an undamaged state.
There are approximately 310 million people in our country. We have 100 million people "not in the workforce". The greater bulk of the jobs being created are low-wage and/or part time jobs that are not compatible with a independent lifestyle in our current socioeconomic model.
In other words, we are currently in a system where resources are becoming more scarce. This trend is amplified by the steadily decreasing availability of usable energy.
Simply put. Immigration is a policy for appropriate to an expansionary (e.g. anabolic) system. It is a nightmare for a compressive (catabolic) system.