The 'Great Wall' appealed to the very dumbest of the idiotic 'Conservatives'. At present about 40% of illegal immigration comes in on airplanes. What is the clown going to do, order a travel ban on the world outside of the US borders? Perhaps that should not be put into writing as he is stupid enough do something like that.
He's already doing it. I live 30 miles from the Canada/US border, where cross border shopping is a way of life. Many of my friends are reporting they are being turned away from entering the US for no apparent reason. A number of my friends are cancelling planned trips as a result. These are people who cross the border regularly, and have no reason to expect to be turned away. They're even white Christians, so the idea that it was skin colour or religion is completely false.
People around the world are having similar reactions, as tourist bookings are way down in the US this year. Electronic communications, SKYE, and other means of video conferencing are making saying home easier than ever for business, and why go to the US and risk being turned away and ruining your vacation, when the rest of the world is available.
This is the law of unintended consequences. Business, retail, and tourism will pay the price for Trump's Muslim ban.