What they need is enforcement, not letting people go and hoping they'll show up in court. What they need is sophisticated radar systems like the one the Department of Defense once gave them to fight a plague of ultralight aircraft, or the long-range acquisition-systems optics that give actual geo-coordinates—that stuff would be a game changer, but the military won't share. "I'll be quite frank," Sadler says. "They think this threat just isn't big enough to justify bringing the resources to bear."

He's right, of course. Until Trump, the default consensus among both conservatives and liberals was that zero tolerance cost too much. Liberals wanted amnesty, and conservatives, despite all their talk of securing the border, never wanted to spend the money.

All this bugs a guy like Sadler, the ultimate straight arrow. In his book, rules are rules.

Do not joke with him about letting only the hot Latinas in, because he will give you a deadeye stare. "As a Border Patrol agent, the only hot woman is my wife."

But Sadler's thinking doesn't stop with the hard line of the law. Several times he says that the greatest commandment is to love our neighbor as ourselves. When he tries to look at the big picture, he sounds almost pained. "When you have a draw that's based on folks' well-being—I mean, there are people that aren't eating three square meals a day down there—you're always gonna have those people who are willing to take the chance. The solution is Mexico. The government of Mexico becomes a government for the people. That's the solution. Then you won't need a wall."

"If it's a thousand feet high, they'll go underneath it. If it's a thousand feet deep, they'll go around it. If it's a thousand miles long, they'll go through it."

With this, I venture a personal question. Should I have asked my Guatemalan gardener for papers?

"I don't know," Sadler says. "You're a private citizen. I don't ask the guy who's gonna work on my truck if he's got documents or not."

What about walking the Mexican hippie across the border?

There, Sadler draws the line. "That's alien smuggling. Title 8-U.S.C.- Section 1324. It's a felony."

"I was eighteen."

He controls a look of faint dismay. "You were eighteen," he says, "and ignorance of the law is no excuse."

A year and change after leaving the Border Patrol, he still grinds his teeth every night.

Drive on, merica, and the border will travel alongside you like a wound. Drive down the old Texas highway past Marfa, past Alpine, past Marathon, down to Big Bend National Park, where the naked mountains of West Texas tumble into the Rio Grande. No landscape in America is more remote and sublime. When the man who fought to make this a national park saw it for the first time, he said it was as close as he'd come to the mind of God. The vast scale feels eternal, unworldly. On the Mexican side, a massive cliff of orange stone rises fifteen hundred feet high and goes on for miles, monumental and forbidding. The river took millions of years to carve that cliff.

A sweet old park volunteer sighs. "People who support the wall have never been here."

In the eighties, she says, they used to joke about Sandinistas trying to climb down all that vertical stone. How out of touch the people back in the cities were with the scale of things down here! "SPACE," the poet Charles Olson said. "I spell it large because it comes large here." That's the essential fact about America, which people looking at screens tend to forget.

At the base of the cliff, the Rio Grande is just a glittering ribbon ten feet across. Skip a stone and it lands in Mexico. Take a boat down this river through the Santa Elena Canyon and pitch a tent in the stretch where the cliff goes up on both sides, fifteen hundred feet straight up. Look up from your sleeping bag and see a river of stars—Big Bend is also a dark sky preserve, one of the rare places in the world where a premodern starscape can still be seen. A wall on that cliff so far above would be a cosmic joke, a child's scribble on the face of creation. It would be the boot of big government on the neck of a swan, and the people who say they want it would be the first to start tearing it down. There will never be a wall here.

The scale of natural barriers, such as Big Bend National Park, mocks even the largest possible wall.

Which means there is only one alternative: Fill in Big Bend! Blast down the Baboquivari Mountains! Cede the littoral areas of Texas to Mexico! We cannot let our kind hearts and monistic yearnings dissuade us from the great task ahead. Build that Wall! Put a road down the middle and rotating turrets every hundred yards, buy the latest in motion detectors, put in gyms for the troops so they stay in shape, plate the whole thing in gold! How beautiful that we respond to troubled times with a great new project, a massive new dream! Goodbye Frontier, hello Wall! Let the migrants fear to approach! Let them tremble in awe! When the climate refugees start to come twenty or thirty years from now, imagine the heroic songs we'll sing of the Guardians of the Wall and their last great battles. Hit me with your best shot!

Trump has brought us the gift of clarity. To save the border, we must destroy it—or we must give up the beautiful dream of independence we once declared and bind ourselves ever closer to a world in deep trouble.

There is no other choice.