Starting with Franklin Roosevelt, U.S. presidents have worked to heal those historical grievances and build a closer, more mature partnership. But now, President Donald Trump’s talk of sending in troops to deal with “bad hombres;” building a wall between our countries; imposing a 20% border tax, and re-negotiating the North American Free Trade Agreement in a way that helps the U.S. while hurting Mexico – threaten to return us to the bad old days. This stance won’t just hurt America economically. If we humiliate Mexico, a proud and important country, we will undo years of progress; stoke anti-American sentiment; and possibly turn a friend into an enemy – making both countries less secure.

I say this as an American citizen who has seen the relationship from both sides of the border. As an impulsive young college student on the G.I. Bill in the early 1950s, I was inspired by the movie The Treasure of the Sierra Madre to move to Mexico in search of gold. Mexicans joked that I was the only American who’d ever swam the wrong way across the Rio Grande.

I never did find gold – but I did find manganese. It helped me build a global mining business. My customers included the U.S. government, which needed our manganese for its strategic stockpile. For decades, I lived and worked among some of the most famous artists and intellectuals in Mexico, along with old miners, prospectors, and working-class Mexicans of all backgrounds. What I found were people willing to work hard to create a stronger and more prosperous future for their country.

After signing NAFTA in 1993, America’s partnership with Mexico – our third-largest trading partner – helped build a nation where its citizens don’t have to go north to have a future. Contrary to Trump’s alternative facts, illegal immigration from Mexico has been falling since 2009, as a Washington Post article recently reported. Mexico and the U.S. have worked to share intelligence and fight drug trafficking and transnational crime. The U.S. has also relied on Mexico to stop between 200,000 and 300,000 undocumented immigrants from entering Central and South America before they ever reach the U.S. border.

By putting Mexico in the crosshairs, Trump threatens to halt all of that progress. One idea that Trump is considering is a 20% border tariff against imports from Mexico to pay for a southern wall. As many wonder how the tariff could get passed along to U.S. consumers in the form of more expensive items in the grocery store and at Wal-Mart, U.S. Sen. Lindsey Graham may have captured the sentiment best in a recent tweet. “Simply put, any policy proposal which drives up costs of Corona, tequila, or margaritas is a big-time bad idea. Mucho sad.”

But there’s far more at stake in our relationship with Mexico. Having a prosperous, peaceful, and friendly neighbor along our 1,900-mile southern border is vital to America’s national security. What difference does it make when a neighbor is hostile and unstable? Just ask South Korea.

The stronger Mexico is economically, the less incentive there is for residents to cross the border, and the more resources Mexico has to invest in security, development, and institutions – all of which benefit the U.S. The answer to making America great again is not to make Mexico more poor. President Trump’s position has already driven the peso to a record low against the U.S. dollar. More isolation could tank Mexico’s economy – ironically, creating precisely the conditions that could drive undocumented immigration through the roof.

In just about two weeks as president, Trump has managed to bring old resentments back. His threat to send the U.S. army to Mexico reminded me of an experience I had in the central Mexican village of Charcas in the mid-1960s. With my business more established, I had helped build a school there and visited a classroom one day, when I saw a map of North America in which the U.S. looked much smaller. Meanwhile, Mexico stretched over the entire American West. As I gazed in wonder, a little girl looked up and asked: “Señor Weiss, why did you steal half our country?”

She was talking about the half Mexico had lost in the Treaty of Guadalupe Hidalgo that had ended the Mexican-American War in 1848, which the map represented. That legacy is a big part of why Mexico has often had a difficult relationship – to say the least – with its powerful neighbor.

Former Mexican President Vicente Fox says Trump represents the return to that time of “the ugly American” and the “hated gringo.” Mexican President Enrique Pena Nieto, who has instituted difficult but crucial reforms supported by the U.S., has seen his approval ratings essentially tank after meeting with Trump. Meanwhile, populist and extreme left-winger Andres Manuel Lopez Obrador, who has been called Mexico’s Trump, is gaining ground for the 2018 presidential elections.

What can we do? I agree with The Economist’s recent suggestion on how to handle a bully. Mexico should highlight its many positive contributions; try to influence Trump to re-negotiate rather than scrap NAFTA, and strengthen Mexico’s domestic economy.

Mexico should also open regular channels with some of the Trump Administration’s more practical officials – like newly appointed U.S. Secretary of State Rex Tillerson and U.S. Secretary of Defense James Mattis. In Mexico, U.S. Ambassador Roberta Jacobson – a career diplomat – should focus on public outreach to show that our president’s disrespect does not represent the American people.

And for the rest of us in the U.S., we should all watch a 2004 film directed by Sergio Arau called “A Day Without a Mexican.” It imagined what would happen in California if Mexicans suddenly disappeared from every job. The result was chaos. The film’s message? We should appreciate what we have before it’s gone.

To do otherwise wouldn’t just be mucho sad – but mucho dumb.

Stanley A. Weiss is a global mining executive and founder of Washington-based Business Executives for National Security. His memoir, “Being Dead is Bad for Business,” will be published by Disruption Books on February 28, 2017.