On May 10, a tanker with a full load of Russian crude oil made its way across the Atlantic Ocean and docked in Cuba — the largest petroleum shipment from Russia to Cuba since the Cold War. The previous October, Russia’s defense minister announced Moscow was considering reopening military bases in Cuba — its first official return to the island since 2002. The Chinese are getting in on the action as well: China is both Cuba’s largest trading partner and the largest holder of Cuban government debt. The Chinese telecommunications firm Huawei is in direct competition with Google to provide internet access throughout Cuba — a high-stakes commercial battle that could determine whether Cubans have access to an open internet or one controlled by the government.

The Cold War might not be back, but Cuba has returned as a national security battleground as Russia and China increasingly engage with Havana and seek influence on an island less than 100 miles from the U.S. mainland. But since Donald Trump took office, the U.S. has been sitting out this fight.

Former President Barack Obama’s historic opening to Cuba didn’t just create an attractive market to American companies. It also enhanced America’s national security, reshuffling regional geopolitics in our favor, increasing border security and expanding access to counterterrorism intelligence. In fact, the past two years of direct engagement with Cuba have had more success in protecting our border, bolstering our influence in the region and preventing adversaries from threatening our security than the six previous decades of attempted isolation.

But since Jan. 20, all engagement with the Cuban government has been halted as the Trump administration conducts a review of its Cuba policy, potentially rolling back the Obama-era reforms and closing off all diplomatic communication with Havana. Such a move wouldn’t just set back U.S. policy goals with Cuba; it would also make the U.S. less safe, allowing foreign adversaries like China and Russia to gain a foothold in our backyard and making our border less secure. For a president committed to an “American first” agenda who is willing to spend billions of dollars on a border wall, closing ourselves off from Cuba would be a shockingly dangerous decision.

We should know: We both served in the American armed forces for over three decades and always kept a watchful eye on Cuba. Looking back on our long careers, it was with some surprise that we found ourselves in Cuba in March as a part of a delegation led by the American Security Project, a nonpartisan national security think tank with which we both are affiliated. The trip’s goal was to gain insight into U.S.-Cuban relations and build confidence between our countries. If someone had told us as young officers we would someday be in Havana, we would have expected to have been a part of an invasion force, one that the Pentagon had long planned as a contingency during the Cold War. Instead, we were peacefully welcomed by the government and people of Cuba.

We have spent our lives guarding America’s national security in every corner of the world and have seen firsthand the policies and initiatives that worked and those that did not. What we saw in Havana was that the U.S. embargo, blocking all trade and investment with Cuba for the past 55 years, has not worked. It has failed to isolate the Cuban government, failed to regain any nationalized property and succeeded in giving an excuse to the Castro government for its abuses and economic mismanagement. The embargo continues to impoverish a people who are naturally drawn to the United States.

Yet, this failure extends beyond the backwardness of the regime in Cuba. The embargo has also weakened U.S. national security because it prevents almost any business that wants to work in the United States from trading with Cuba. In other words, if you want to do business in America (and are not in select industries like farming or medicine), you have to avoid the Cuban market. That has given a huge opening for our adversaries to gain influence in Cuba, starting with the Soviet Union’s aid to the Cuban government. Since the Cold War ended, Venezuelans and Chinese have propped up the Cuban economy by providing subsidized oil or buying distressed Cuban government debt. This support has allowed the Castro regime to survive U.S. sanctions.

On a more tactical level, the embargo prevents the Cuban government from buying the most sophisticated airline security equipment for its airports, meaning that screening procedures for flights from Cuba to the United States may not meet our high standards.

Of course, Cuba is no longer as big a security issue as it was during the Cold War. But Russia and China still view it as an important theater, a place to gain influence and access near the U.S. coast — just as the U.S. seeks influence with countries near Moscow and Beijing. Obama’s opening to Cuba, which re-established diplomatic ties between the countries, expanded Americans’ ability to travel to Cuba. It also gave U.S. companies limited ability to do business on the island and demonstrated that the U.S. was turning the page on a long history of American intervention, reassuring other Latin American countries and pushing back on Russian and Chinese incursions.

Engagement with Cuba was already paying dividends for America’s security, even without the end of the embargo. Prior to Jan. 20, our two countries signed 22 individual memoranda of understanding on everything from how to re-establish direct mail to how to work together on cancer research. Of those 22 agreements, nine directly addressed national security, including on air travel security; countering narcotic smuggling; cross-border law enforcement; and maritime borders and security. This engagement was only going to grow stronger, with several government-to-government meetings on security-related issues scheduled.

Furthermore, since diplomatic relations were re-established in July 2015, the Cuban government claims to have provided information in support of more than 500 U.S. counternarcotics operations and identified 34 human smugglers. At a June 2016 Counterterror Working Group Meeting, combating terrorism in the Caribbean region — from which hundreds of foreign fighters have traveled to join ISIS — was the key focus.

During our trip, we saw firsthand the Cuban government’s commitment to cooperating with the U.S. on security issues. The delegation met with various departments and ministries across the Cuban government and discussed in detail specific areas for U.S.-Cuba cooperation in support of shared security including counterterrorism, cybercrime, combating human trafficking, and immigration and border security. While we may not share governing philosophies, we share the goal of a more prosperous, healthful and peaceful world.

Make no mistake, the Cuban government is in firm control of the nation, and we are clear-eyed about Cuba’s history on human rights. However, its willingness to engage with the United States on equal terms can only motivate and encourage transformational social and economic thought over the long term. A key reality we and many of our former colleagues have come to learn is that imposing our norms and processes on other societies detracts from our strategic interests. The terms “freedom” and “prosperity” have different meanings and generate different expectations across societies.

Trump has promised to put America first and to secure the U.S. borders. But there can be no such security if he rolls back the opening to Cuba. Our elected leaders must continue the process of normalization with Cuba and not let the momentum fade. America can become stronger, safer and more prosperous by means other than military force. The rapprochement between Cuba and the United States has been a great lesson in how effective diplomacy can build national security in the 21st century.

Maj. Gen. Paul D. Eaton served in the U.S. Army for 33 years, including operational assignments in Iraq, Somalia, Bosnia and Albania. Brig. Gen. David L. McGinnis served in the Army and New York National Guard for 29 years, including two combat tours in Vietnam.

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