The San Diego sector of the border wall on April 25, 2018, in California. (Carolyn Van Houten/The Washington Post)
Melissa J. Gismondi is a historian and journalist. She holds a Ph.D. in North American history from the University of Virginia.

On Saturday, the partial government shutdown became the longest in U.S. history, surpassing a 21-day impasse between President Bill Clinton and Republican House Speaker Newt Gingrich in 1995 and 1996. From a historian’s vantage point, the length of the shutdown is unique, but the contentious issue at its heart — President Trump’s pursuit of a wall on the U.S.-Mexico border — is far from surprising.

That’s because the obsession Trump — and many of his supporters — have with the wall speaks to a paranoia about borders, outsiders and threats of “the other” that runs deep in U.S. history and culture. It’s as old as the frontier mythology that defined America from its start, and although Trump has seized on it, it’s likely to continue long after this particular stalemate.

That obsession with the violent fortification of borders is what the renowned scholar Richard Slotkin talked about in his landmark trilogy on the mythology of the frontier. In “Regeneration Through Violence,” “The Fatal Environment” and “Gunfighter Nation,” Slotkin charted the social and cultural anxiety Americans have had about claiming, defending and taming lands that were never their own. This anxiety, Slotkin argued, manifested itself in cherished myths about the significance of violence in fortifying borders and excluding the people who live beyond them.

History is always a push and pull between continuity and change. And you’ll find a lot of differences between how 17th century Puritans, for example, imagined the frontier and how Trump talks about the issue. But there are important similarities, too.

Like many before him, Trump latches onto the belief that the frontier — the imaginary line between civilized and lawful America and the uncivilized and lawless societies that border it — poses an explicit threat to Americans, specifically women. The vulnerability of white women often lies at the heart of this myth. Violent crimes against them, particularly those that are sexual in nature, are used to justify national vengeance and defense. And the ability of the nation to protect women works almost as a barometer, alerting the male powers that be when the frontier has been most egregiously “violated.”

This was a common trope in the early 19th century, when future president Gen. Andrew Jackson justified his invasions of indigenous territories by arguing that failing to do so would threaten American lives. These invasions continued the centuries-long process of marking out and fortifying America’s borders. Waxing poetic, Jackson tugged at emotional heartstrings by relaying stories of the kidnapping, rape and murder of American women by those who crossed into the United States illegally — or, as Trump has put it, who had “violated our borders.”

In 1812 and 1813, for instance, Jackson and his supporters latched onto the story of an attack along the Duck River, in western Tennessee, near the border with the Chickasaw Nation. Newspapers sensationalized the story, providing readers with gruesome details of how a white woman known only as Mrs. Manley was murdered, and possibly raped, by unidentified indigenous warriors. Another woman, Martha Crawley, was kidnapped and taken into indigenous territory, where newspapers falsely accused her captors of raping her.

The story captivated Jackson and his supporters. “Your frontier is threatened with invasion with the savage foe,” Jackson told his troops in an effort to rally support for an illegal invasion into indigenous territory. “The wretch who can view the massacre at the mouth of Duck River, and feel not his spirit kindle within him and burn for revenge, deserves not the name of a man.” Future Tennessee governor William Carroll echoed Jackson’s argument, asking, “Who among you can sit quietly at home and hear the story of savage butchery?”

The story, and the rhetoric, was soon given a national audience when it was picked up by Hezekiah Niles, editor of the widely distributed newspaper the Niles Weekly Register. “The attack,” Niles attested, “is but a type of what is transacting on many parts of our frontier.” The solution? Swift victory in the War of 1812, which many Americans saw as the only way to strengthen the new nation’s borders and protect its civilians from attacks by indigenous nations allied with the British.

It’s in this spirit that candidate Trump notoriously called Mexican migrants rapists, a comment he doubled down on in a 2018 interview with CNN’s Don Lemon. “Somebody’s doing the raping, Don. I mean somebody’s doing it. Who’s doing the raping? Who’s doing the raping?” And it was also in this spirit that Trump referred in his Oval Office address this month to the rape and murder of Air Force veteran Marilyn Pharis “by an illegal alien with a long criminal history.”

“How much more American blood must we shed before Congress does its job?” Trump asked.

Like Jackson before him, Trump failed to cite important information that contextualized the crime. Jackson didn’t consider the fact that the Duck River attack was part of an extended campaign by indigenous nations to combat the illegal invasion of white settlers into their ancestral homelands. Likewise, Trump failed to mention that Pharis was sexually assaulted and killed by two men: one who had indeed entered the country illegally, and another who is a U.S. citizen. Nor has Trump — a man who admitted to sexually assaulting women on tape and mocked Christine Blasey Ford’s testimony about her alleged sexual assault during Brett M. Kavanaugh’s Supreme Court nomination hearings — shown any indication that he cares about sexual violence when it’s not perpetrated by men who enter the country illegally.

Before Trump, many presidents used stories about “savage foes” preying on innocent Americans in violation of federal borders to help launch invasions into sovereign territories. Right now, an invasion into Mexico or any one of the Central American countries migrants flee from seems unlikely, despite the United States’ long — and recent — history of proxy wars throughout the region. But for Trump, the wall serves a similar purpose: It’s an emotional issue, one that speaks to deep-seated patriotism surrounding America’s ability to defend itself from threats that are sometimes real, but are mostly imagined.

So why is all this important to keep in mind? The answer goes back to Slotkin’s emphasis on the importance of myths in the American psyche. “A people unaware of its myths is likely to continue living by them, though the world around that people may change and demand changes,” Slotkin wrote. He added that a history of viewing America as the beacon of global freedom and democracy makes it particularly hard for Americans to see these stories for what they are: myths.

But seeing them and paying attention to them, however irrational they might be, is a must, Slotkin said. Failing to do so can leave you blindsided by the chaos and violence national myths often produce. Right now, that chaos is the violence that’s unfolding at the U.S.-Mexico border and in a government that’s been partially shut down for weeks. It’s hard to predict how the shutdown will end, or what will become of the wall. But even if Trump gives up this particular battle, the centuries-old myth doesn’t seem to be going anywhere.