A recent news story has a presidential candidate flirting with the idea of building a wall along the U.S. border—the northern border. His explanation:
Walker has long said that securing U.S. borders, especially the southern border with Mexico, is not only a deterrent to illegal immigration but also a way to ensure that terrorists and international criminals do not enter the country.
The U.S. hosts about 75 million tourists each year, coming from a wide variety of countries. Does anyone seriously believe that we can filter out from that flood one, or ten, or a thousand bad guys? All a competent terrorist needs is a passport in a name that isn't on a list of people to keep out. I do not know what country in the world is currently the least expensive source of bogus passports, but I would be surprised if the price was high enough to discourage someone supported by ISIS or al Qaeda or ... .
As in too many other cases, the underlying logic is:
Something must be done.
This is something.