After six rounds of talks, uncertainty cloaks the future of the North American Free Trade Agreement (Nafta). Most of the debate centers, quite naturally, on trade. But another aspect goes almost entirely ignored: how Nafta affects national security.

Perhaps that's because it's much easier to tally up the benefits of the trilateral agreement from a trade and financial standpoint. Much has been said and written to address the profound economic setback a withdrawal from Nafta would be for the U.S., Canada and Mexico.

Our Nafta partners are the largest buyers of U.S. exports, which enables U.S. manufacturing to compete better with Asian producers. American farmers and manufacturers alike are the beneficiaries of the 14 million U.S. jobs that Nafta supports. The benefits are plentiful and enjoyed by all parties.

Yet the national security implications of this decades-long agreement often go untold. The termination of Nafta by President Trump would undercut U.S. broader objectives not only with Mexico and Canada but undermine our national security goals throughout the Western Hemisphere. Nafta is the bedrock of America's regional security interests.

The U.S.-Mexico partnership did not evolve overnight. In the late 1980s, Mexico cast its collective future with the United States. Over more than two decades, cooperation with Mexico has deepened in all aspects of the bilateral relationship. While joint economic security has expanded, American cooperation with Mexican law enforcement to combat organized crime, identify counterterrorism opportunities, and address illegal immigration has reached unprecedented levels. Our Mexican counterparts have worked to make America safe.

A generation of citizens in both countries living under Nafta have benefited by this enhanced cooperation. But as with all relationships, challenges surface where interests diverge. The U.S. and Mexico don't see eye to eye on every issue. And naturally, cooperation can always be enhanced.

Nevertheless, open lines of communications, encouraged by Nafta, have enabled de-escalation when differences have surfaced and good-faith efforts have prevailed. Cross-border cooperation enabled by enhanced law enforcement information sharing is vastly better today under Nafta.

As Nafta established a code of conduct for effective trade, it also created a much-needed framework for improved rules of engagement on national security matters as well.

One specific setback triggered by a Nafta withdrawal would be the doomsday scenario for the U.S.: a reduction in Mexican cooperation targeting illicit drug trafficking. For political reasons, the decline would be swift from Mexico and painful for the U.S.

America's opioid epidemic makes this an option we should not entertain. The scale of the crisis is unprecedented. In 2016, overdoses killed more than 42,000 people, a sixfold increase from 1999. Heroin's deadlier synthetic counterpart fentanyl is responsible for over half of overdose deaths. The Drug Enforcement Administration (DEA) estimates that 93% of U.S. heroin reaches the U.S. via Mexican criminal organizations and virtually all fentanyl is from China and Mexico.

Withdrawing from Nafta not only would result in an increased body count, it would shut down the administration's broader hemispheric agenda. Specifically, there would be no fewer than five negative outcomes if Nafta is terminated by the Trump administration:

• America's message to the Western Hemisphere would be of an unreliable trading partner and undependable nation on vital regional issues. In jeopardy would be the sharing of counterterrorism information, counternarcotics cooperation, countering human trafficking, and undertaking joint intelligence efforts.
• Credibility of U.S. regional leadership would also be undermined. If the Trump administration is considering any single big initiative to enhance hemispheric cooperation, that outreach would most likely be dead on arrival.
• Foreign adversaries will capitalize on this vacuum. Chinese principally and the Russians to a lesser extent will expand their economic and political interests in Latin America and the Caribbean. China has already diversified its investments in Latin America beyond oil and mining into other industrial sectors. At a time when the U.S. already faces challenges caused by Chinese and Russian financial encroachment, an abdication of American leadership is counterintuitive. It will amplify Chinese and Russian efforts in a region far more inclined to naturally look to the U.S. for partnerships and investment.
• American influence will be weakened in efforts to resolve the Venezuela crisis, created by the despotic regime of Nicolás Maduro. The Trump administration is on the unprecedented cusp of establishing a common front alongside the democratically elected governments of Latin America to isolate Maduro and his cronies while boosting support for the democratic opposition within Venezuela. A drop in America's regional perception would derail these efforts.
• U.S. efforts to effect positive change in Cuba will suffer setbacks. American influence will wane in efforts to build partnerships with Latin American countries in countering Cuba's continued failure to institute democracy and address the deplorable human rights conditions on island.

Latin America and the Caribbean offer ample opportunities for enhancing U.S. influence. The gateway for that influence is a successful renegotiation of Nafta. Conversely, President Trump's unwarranted withdrawal from Nafta would create serious challenges from any and all U.S. initiatives at the bilateral or multilateral levels in the region.

A full-court press is needed to place our collective efforts behind an enhanced Nafta agreement. A withdrawal from the treaty will place the U.S. at a significant disadvantage throughout the region in all efforts to build cooperation.

Our fundamental policy objectives of building strong institutions that promote the rule of law, foster free economic markets, and counter nefarious forces in the hemisphere from transnational organized crime organizations to state actors who wish to undermine the U.S. is within grasp.

Mr. President, the portal for achieving those objectives is a successfully renegotiated Nafta.