Nearly a month has passed since U.S. voters chose their next president, and over the past few weeks it has become a little clearer how the policies of President Donald Trump will differ from the promises of candidate Trump. As we have seen since January 2009, when newly elected President Barack Obama received the Nobel Peace Prize for his campaign pledges of change and hope, reality has a way of constraining a leader's ability to effect real change. And more often than not, the policies that presidents put into practice look very different from the ideas they put forth on the campaign trail.
The same will probably be true of Trump's vow to seal the U.S.-Mexico border by building a wall. One of the biggest problems with this proposal is that the flow of illegal immigrants and contraband between the two countries is not a simple matter of physical security, international...