With the flourish of a pen on an executive order the afternoon of his first day in office, President Biden radically changed the relationship between Mexico and the United States — especially at the border.

Largely returning to the status quo ante of the Obama administration, Biden halted construction on the controversial border wall, established a temporary moratorium on deportations, and is, if the words of the migrants caravans marching up from Central America are correct, opening the border again.

But are we really returning to the regime of a few years ago? Or has the reality of the border so radically changed over the intervening years that these new rules may instead produce a whole new set of unanticipated — and even destructive — results?

Late last year, I published a new book, “El Tercer Pais,” “The Third Country.” In writing it, I set out to look past the stereotypes to see what was really happening today at the border and in that narrow strip of land on both sides of the wall in Tijuana and San Diego. I talked to everyone from business and community leaders to everyday citizens on both sides.

What I found shocked me. For one thing, I discovered the existence of a distinct region — the “third country” of my book’s title — composed of the strip of land, in some places just blocks wide, straddling the border. Here was a new culture, a hybrid of North and South, populated by people accustomed to passing freely back and forth from one country to the other: Tijuana students going to school in San Diego. American patients heading south to see San Diego doctors at state-of-the-art “medical tourism” hospitals in Tijuana. Executives of American corporations crossing over to visit their maquiladora manufacturing plants just a few hundred yards away on the other side.

None of that fit standard stereotypes about the border: hordes of undocumented immigrants swarming over the border, families risking their lives running across the freeway (as the notorious signs warned). Indeed, everywhere you look holds a surprise. For example, Tijuana, once little more than border village, now has a larger population than San Diego.

A visit to a maquiladora, with its robotic assembly lines and computer-assisted manufacturing, explodes the notion that only the U.S. has sophisticated production, while Mexico remains exclusively a domain of craftsmanship. Indeed, just about every pacemaker sold in the U.S. was built in Tijuana.

How has all of this happened? It is the product of more than 30 years of a grassroots effort by citizens of both great cities, recognizing they had more in common with each other in many ways than with their capitals thousands of miles away. That their economic health depended upon the success of each other. And that, ultimately, they shared a common fate. Politicians and bureaucrats on both sides have had no choice but to follow.

And the wall? It is unmistakable, but also increasingly irrelevant. With a FastPass, you barely need to slow down to cross the border. Maquiladora managers will quietly tell you that they don’t mind the wall’s presence: It keeps in Mexico the very migrants they are so anxious to hire. The Tijuana middle class? Their favorite place to shop is a giant outlet mall that abuts the wall … on the San Diego side. And San Diegans? As long as they can move freely into Tijuana to do business downtown — and take advantage of USMCA, the United States-Mexico-Canada Agreement. Besides, if it keeps out the cartels that still makes Tijuana’s poorer outer districts dangerous, the wall — ugly as it is — is welcome.

The Biden administration is promising to fundamentally change the current situation at the U.S.-Mexican border. Let’s hope that before it does, it first understands just what that situation is today.

Michael S. Malone is a Silicon Valley author whose latest book is “El Tercer Pais: San Diego & Tijuana Two Cities, Two Countries, One Community.”