President Donald Trump made one particular promise a lot while on the campaign trail: under his aegis, America will build a "great" wall.
Just five days into his presidency, Mr. Trump took the first step toward keeping that promise, signing off on an order to get the wall built.
Mexico's reaction was swift. Mexican President Enrique Peña Nieto canceled plans to meet with President Trump in Washington next week. For his part, the President indicated if Mexico wasn't willing to pay for the wall, he wasn't willing to meet with Pena.
This back and forth over the border is nothing new. Border expert Deborah Kang says it actually started around 1917.
"You had the onset of World War One and fears about the entry of subversives — specifically, German spies," says Kang.
Kang says those fears were stoked after the discovery of a document known as the Zimmerman Telegram. In it, a German foreign minister appeared to ask Mexico to enter the war on the side of Germany. If the Germans won the conflict, he said, they would help Mexico regain territories lost during the US-Mexico War.
Kang is the author of the new book, "The INS on the Line: Making Immigration Law on the US-Mexico Border 1917 to 1954." She says the Telegram exacerbated xenophobic sentiment in the country, setting the stage for efforts by the Immigration and Naturalization Service (INS) to erect barriers in the 1920s.
By 1954, the INS was flying high: the mass deportation campaign known as Operation Wetback had produced the desired result. So much so, that the department garnered extra funding from Congress to erect more fences and walls along the southern border. Kang says this also marked a turning point in the national discourse:
"You see the INS and the federal government talking about building not just a single chain link fence, which is what you had in the early 20th century, but layers of fencing surrounded by patrol roads, Jeeps and surveillance towers. This sounds like the kind of system that we have in place today," Kang says.
Looking at modern efforts to secure the border, Kang says history offers an idea of what works and what doesn't. In regards to walls, Kang channels former Arizona Governor Janet Napolitano:
"If you show me a 50-foot wall, I'll show you a 51-foot ladder," Kang muses. "She and others have made a point that if you build a wall, individuals will always find ways over them, under them, and through them."
(This post has been updated.)