The image and the costs of a Berlin-like wall or a Great Wall of China is something that the American people have not accepted to date.

Not only are the numbers of migrants entering the United States at the lowest levels in a generation, but they are now largely Central American. Four out of five border-crossers detained in South Texas are Guatemalan, Honduran or Salvadoran. They are driven by violence and poverty in their home countries and the desire for family reunification.

There have been enormous advances since 9/11 to build a very robust set of targeting procedures and watch lists to screen travelers coming to the United States. The National Targeting Center in Virginia run by Customs and Border Protection checks the background of every traveler who seeks to enter the country.

America should be working more with the Mexicans to prevent the flow of guns going south into Mexico that have fueled so much of the violence there, and the smuggling of cash and the money laundering that transnational criminal organizations have instituted in North America, including in the United States.

People in our so-called Rust Belt have lost out, and politics and society have not been responsive either in providing the kind of additional support they need or to retrain them for jobs that are being created in the new economy.

We must recognize that this massive economic bloc that's emerging in North America cannot be accomplished unilaterally. It must be accomplished in partnership with Mexico and Canada. And we have to work together to secure the continent in order to keep dangerous people and dangerous things out and strengthen perimeter security on a continental basis.

We need to realize that the economic situation between Mexico and the United States is not just one in which we trade with one another. We make things together. We have shared production platforms. Cross-border trade is part of a single production process, and while apparently the Trump administration will seek to re-examine elements of that production platform, it is what it is and won't be easily dismantled.