Generally, you can go and ask the build-the-wall crowd and the anti-build-the-wall-crowd various questions over immigration, the 'Mexicans', legal terms and ethics.....but never get any real comforting answers.
So I'm a history guy, and I like how history relates lessons learned....some wise, and some pointless.
The Chinese started a wall operation in the period of 700 BC. When it was finally done.....roughly five-hundred years would have passed. Course, this wasn't a wire fence, or modern technology type situation.....it was brick and cement. What the Chinese wanted....was a wall that stood the issues of time. I should also mention that this was a 13,000 mile wall....way more than from you'd want from Texas to California.
Chinese historians will tell you....in a blunt way....the way achieved everything desired. They will also note that it was a public project, and employed folks of the region....keeping them happy, occupied and fulfilled. The foreign guys stayed out for the most part (they were failures of the wall), and some folks did climb over.....but without horses.....it was a bit difficult to march on and get somewhere.
The East Germans built two walls. One was the border fence along the front between East and West Germany. The other was the circling fence or wall that was put up in Berlin. The evil West Berlin folks, with no inhibitions or control of desires were kept from the "people of perfection" in DDR (the Democratic folks who liked Communism).
If you go back 1,500 years across Germany itself today, you will find evidence of hundreds of walled cities and towns. The walls were built to keep trouble-makers out, and protect folks during periods of incursion. Generally, the walls worked unless the trouble-makers were creative and found ways to break the walls down.
Generally, if you build a wall....someone will come along and say they can conquer the wall. People take pride in overcoming walls. If you built a seventy-foot tall wall.....there'd be some guy to come along real quick and find five ways of getting over the top of that wall. The guy might even write a book about the experience.
What I see from Trump-the-candidate....is that he might actually get elected and be part of the wall-crowd. Then he'd arrive in DC to find that the Republicans really can't find any enthusiasm or willingness to put money into a wall. The Democrats will just stand there.....gleefully smiling and not having to say anything because the fraudulent Republicans are doing all the work for them.
Trump would stand there for around six minutes....listening to the reasons why they won't fund it, and then say fine.....he'd just assign the US military to the task and just start yanking them back from South Korea, Europe and the Pacific.....to build the wall. Republicans would go on TV and chat about how you need to build a wall, but only in the right way, at the right time, and with the right plan. This would consume an entire weekend of political chat shows.
Generally, I don't think the wall would do an awful lot because folks would just seek out smarter ways.....maybe like digging a tunnel or just taking a rubber boat from Mexico to the Texas coastline (kinda like they do from Libya to Italy today). The thing is....we've gone so long in this fake agenda business, that we really don't believe much of anything that's said now.....by either party.
Being against the Mexicans? Well.....I'd be all for a wall built up along the Canadian border too....except I know that the Canadians don't really care much to illegally cross (there might be forty a year that do it illegally). The eventual problem I see is that 300,000 Nigerians or Chinese guys might also get the idea that it's awful easy......sailing to Mexico, and then just hiking across. Would we be just as happy to see them crossing the border as the Mexicans? I have doubts.
So, maybe at the end of the 2016 election.....we might accidentally elect Trump as President and start on some wall. We might even call up some Chinese guys or former East German engineers to ask how you build a good wall.