Pakistan, Aug. 16 -- There was a time when the United States and Canada were so deeply intertwined that it was almost impossible to tell them apart. The world's longest undefended border felt like an open gate between two homes. In 2018, during a visit from France to Canada, I stayed with my sister and later traveled with my family to Niagara Falls to see my brother-in-law in Michigan. At the border, our documents were checked briefly, but my brother-in-law's American ID allowed him to pass without delay. It was a small yet telling example of the mutual trust and convenience that marked the relationship between the two neighbors. Canada's warm hospitality toward U.S. visitors and the respect they received mirrored the dignity the United S...