Kind of hard to close a border we don't have a fence over. The illegal stuff is what we are worried about and closing the border will not stop that when it just has to find the gaping hole in the wall.
The threat to close the border has less to do with trying to stop illegals as it does with leveraging the above-board businesses to get aboard the issue of border security. Which will ultimately break the hold the illegal institutions have on Mexico and our southern border.
Long term solutions versus short term feel-goods.