One current PresCand promises to build a "big, beautiful wall" to keep out of the USA those whom the FedGov has not yet approved, yet who wish to enter and offer their labor at prices lower than those already here. He can expect the votes of those already here. His opponent makes no such promise, because her party prospers from the votes of people who depend on handouts of money stolen by government, so she favors more dependents and thinks illegal aliens are a useful source. Such is the sick basis on which many voters will vote, a few weeks from now.
There is, however, a huge wall to limit immigration already in place. It may have cracks and leaks here and there, but Trump's wall has already been almost fully built - by governments under all his predecessors, especially during the last century. I encountered it myself, last Saturday evening.
This existing wall consists of a complex series of documents and proofs that an individual is entitled to enter the country. Upon arrival from abroad, these are scrutinized by agents of government, now called the Customs and Border Protection, CBP. I've been coming and going since the late 1960s, and the lines of those awaiting scrutiny have always been much longer than those in any other country I've visited, but have gotten steadily worse and now they are horrible. At Boston (Logan) last week there were many hundreds of tired travelers awaiting the scrutiny in a vast hall, similar to this photo.
I emphasize that about three quarters of them were US Citizens, who in the current theory of government have a right to enter the country any time they wish. Yet those lines were just as long as those for foreign nationals. The process took about an hour, including wait time. The uniformed scrutineers went about their labors in a measured and unhurried fashion, often chewing gum and clearly enjoying their status as torturers, demonstrating that government is about power and control, not about "service". In the background were multiple video screens offering clips of typical American life for the benefit of foreigners; baseball, parades, cornfields, even the Constitution; the film makers must have found a copy and dusted it off. The whole scene was Orwellian; the propaganda was on the screen, the reality was all around us, as the absurdity of delay and control. Goebbels' ghost must be ROFLOL.
"Torture" is about right; there was a seething resentment among all being forced to wait, but it was silent. Only those under about 4 years of age gave voice to their dissatisfaction, because they had not yet been conditioned to accept it; adults knew quite well that any vocal complaint would lead to even longer delay, at the CBP agent's discretion; and all of us had arrived after long flights. I'd been up for 18 hours myself, counting time for preparation, travel to the origin airport, going through security checks there, and 8 hours actually in the air. Comparison with a cattle stockyard is close to spot-on.
Yet all of us had perfectly valid documentation, as specified by government.
"9/11" is the excuse used for this monstrous treatment, even though the principle was in place long before those heavily-provoked attacks took place. Some victims of FedGov foreign policy struck back viciously, and ever since, ever more detailed control has been used over those wishing to cross the government's line on the map. 9/11 was a vast boon to the government industry, so much that it makes one wonder whether the whole thing was a false-flag event. I don't think it was, but government has taken full advantage of it and will no doubt take a good deal more before its day is at long last over.
After that happy day, the coming zero government society will have abandoned the pretense that "government" owns anything at all, much less a "domain"; all property including land will be possessed by true owners, some of whom will be in the business of welcoming visitors and other travelers. They will provide places for aircraft to land, for a fee to the flyer, and space for cars, buses, trains and taxis to convey passengers onwards, so as to encourage customers to use their facility. There will be no "foreign policy" to generate resentment abroad, and hence no danger of anyone wreaking revenge, hence no need to know who is coming or going or to examine their papers or baggage. There won't be any "passports" because there will be no government to issue them; anyone will be welcome to come to the Former USA to trade or tour, and foreign governments who turn back FUSA residents who lack a passport will soon learn how valuable it is to trade with us and so will scrap the requirement. Thus will freedom spread.
Walls may work, for a while, for military defense; the Great one in China did serve to keep raiders out of some of the dynastic empires there; but the wall of Jericho famously came a-tumblin' down when God's Israelites marched round and shouted, so they could capture the city and slaughter its inhabitants. Perhaps an earthquake coincided with their siege. The Berlin Wall lasted a few decades, but didn't keep down the resolve of enclosed Germans to escape their Communist enslavers. And the partial Wall to our South has not excluded Mexicans determined to cross it. So generally, walls don't work. Humans want freedom; it's integral to our nature. And for good measure, freedom works.