The American theory of 'a secure border' is only a couple of decades out of date but they will continue with it until there has been at least one more significant exposure of it.
That is, post 9/11 they did a lot of running around and folks are thinking that is working. When you have land and sea borders that the USA have - it's utterly impossible to police them so, once there is another major attack launched form within the country, the USA will be forced to reconsider their approach.