On Saturday the partial government shutdown became the longest in U.S. history, surpassing a 21-day impasse between then-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 — Donald 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 American 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.