The United States needs immigrants because the population would be declining. Normal citizens can't handle more kids due to economic issues (ask a millennial).
The best policy is to get rid of everyone who does not want to be here and replace them with people who do.
There are millions of traitors and subversives that need to be deported and replaced by Central Americans which show far more loyalty.
As for walls, what a joke. First walls don't work, ever heard of the Great Wall of China or the Maginot line. Second, border enforcement is far cheaper and easier using mobile forces in conjunction with air surveillance.
We need workers, not traitors.
The problem with knowing everything is learning nothing.
If you don't know what you're doing, find someone who does, and do what they do.