This is what is happening on that front already:

A 2017 executive order barred people from seven countries, including five with Muslim majorities, from entering the country. An older rule put in place during the Obama administration compelled anyone who’d even just visited seven blacklisted nations to obtain additional clearance before traveling to the United States. Even as the Trump administration’s policy has met with legal challenges, it means that the barrier to entering the United States, for many, begins with their data and passport stamps, and is thousands of miles away from this country.

The Trump administration would also like to make it harder for immigrants who’ve received public assistance to obtain citizenship or permanent residence by redefining what it means to be a “public charge.” If the administration succeeds, it will have moved the border into immigrants’ living rooms, schools and hospital beds.

The walls of the future go beyond one administration’s policies, though. They are growing up all around us, being built by global technology companies that allow for constant surveillance, data harvesting and the alarming collection of biometric information. In 2017, the United States announced it would be storing the social media profiles of immigrants in their permanent file, ostensibly to prevent Twitter-happy terrorists from slipping in. For years, Customs and Border Protection agents have asked travelers about their social media, too.

The Electronic Frontier Foundation has said these practices can “chill and deter the free speech and association of immigrants to the United States, as well as the U.S. persons who communicate with them.” In other words, it’s no longer enough to have been born in the right place, at the right time, to the right parents. The trail of bread crumbs you leave could limit your movements.

It’s possible to get a glimpse of where a digital border might lead from China. Look at its continuing experiment with social-credit scoring, where a slip of the tongue or an unpaid debt c ould one day jeopardize someone’s ability to board a train or apply for a job. When your keystrokes and text messages become embedded in your legal identity, you create a wall around yourself without meaning to.

The Berkeley political theorist Wendy Brown diagnoses the tendency to throw up walls as a classic symptom of a nation-state’s looming impotence in the face of globalization — the flashy sports car of what she calls a “waning sovereignty.” In a recent interview for The Nation, Professor Brown told me that walls fulfill a desire for greater sovereign control in times when the concept of “bounded territory itself is in crisis.” They are signifiers of a “loss of a national ‘we’ and national control — all the things we’ve seen erupt in a huge way.”

Walls are a response to deep existential anxiety, and even if the walls come down, or fail to be built in brick and stone, the world will guarantee us little in the way of freedom, fairness or equality. It makes more sense to think of modern borders as overlapping and concentric circles that change size, shape and texture depending on who — or what — is trying to pass through.