The idea was to restore the rule of law, to bring order to a chaotic situation. The results became more and more apparent. Crime rates went down in the border region. Today, the number of migrants crossing is at a 30-year low. That's because of years of bipartisan work on this issue.

Every air traveler entering Mexico is vetted against US databases. The air passenger screening system Mexico has in place involves these checks against US national security and criminal data bases. There are plainclothes US officers stationed at airports in Mexico working with Mexican immigration officials to protect the United States. This joint security program has been in place for at least six years and is a huge asset.

Six million jobs in the US depend on trade with Mexico. Ten border states - six in Mexico and four in the United States - combined have the third or fourth largest economy in the world. Twenty-nine US states depend on Mexico as their primary export market.

The nationalism and the protectionism that was built into the Mexican Revolution in 1910 and that characterized the Mexican attitude to the United States for much of the 20th century were difficult to overcome. But that actually has occurred. And the cooperation, trust and confidence that have been built is not something that should be abandoned without great consideration for the potentially grave consequences to the United States.

We should be wary, particularly with our closest friends and allies, of breaking down the trust and confidence that lie at the foundation of relationships.

The potential of Mexico, Canada and the United States is enormous. We have a combined population of half a billion people; peaceful trade-friendly borders that are the envy of the world; the prospect of energy independence is within reach and will change the geopolitical situation of United States; we do a trillion dollars in trade among the three countries; more than 18,000 American companies are involved in foreign direct investment in Mexico and Canada; an increasing number of Mexican companies are creating jobs in the United States.

I think there's no question that the barriers, the fences and in certain urban areas, the walls, have had an important effect in terms of increasing the manageability and the security of the border. But in fact as Secretary of Homeland Security General John Kelly acknowledged at his confirmation hearing, walls and barriers alone are insufficient to insure security.