Photo: The Washington Post/Getty Images

Donald Trump, the first New York City kid to become president since FDR, will also be the first commander-in-chief to move to the White House from an apartment. True, his 30,000-square-foot, gilt-slathered Trump Tower penthouse is no ordinary pad, but the fact that he lives in the innermost heart of what you might call the inner city means that security arrangements don’t just inconvenience a few neighbors; they screw up a sizable chunk of Manhattan. Fifth Avenue in the 50s is almost always clotted with pedestrians and cars, and this time of year it becomes even more congested as department stores turn their windows into Christmas Barneys-, Saks-, and Dior-amas. But Trump’s election has turned his stretch of Fifth into the urban equivalent of the security line at JFK: Aluminum barriers squeeze traffic into a pair of lanes, sidewalks are blocked off, and pedestrians shuffle past a gauntlet of armed officers.

The city can cope with this disruption for a while. We grumble when world leaders converge on the United Nations twice a year, paralyzing the East Side, but we also recognize that statespeople need their New York fix, too. We know the excitement and irritation of moving aside for the 13-car motorcade ferrying President Obama to dinner at Cosme. But when the president-elect lets it be know that over the next four years he’d like to slip back to his Tower on weekends (because, really, who wants to spend a Saturday afternoon in downtown D.C.?), that will be not a mere annoyance but a state-sponsored takeover of public space.

We’ve seen it so often: Jersey barriers and modular fences, automatic weapons slung across Kevlar vests — the whole visible apparatus of control and intimidation in the name of safety. We become gradually accustomed to the notion that public space is dangerous space, and that all this surveillance and exclusion is for our own good. The World Trade Center is ringed with vehicle barriers and guard booths. The police presence at this year’s U.S. Open in Flushing Meadows–Corona Park was so oppressive that it forced the Queens Museum to close for ten days. Other cities, too, experience temporary lockdowns that segue into permanent conditions. The French embassy in Rome occupies the 16th-century Palazzo Farnese, which is lined with travertine benches where ordinary Romans have lingered to chat for 400 years. Now, guards and bars keep the public away.

Ever since 9/11, architects and planners have looked for more genial ways to minimize potential threats: cameras, of course, but also bollards that look like charming street furniture and public structures that are tougher than they appear. Even so, militarizing the streets has become the option of first resort, establishing a presence that’s as frail as it is aggressive. Paris has been bristling with security forces since the Charlie Hebdo attacks — which didn’t prevent the calamity of the Bataclan less than a year later. The 85,000 soldiers who kept Rio de Janeiro quiescent during the Olympics retreated after the crowds went home — and the military soon found itself in a shooting war with resurgent gangs. Blatant security works like a burglar alarm sticker on a front door: It announces to aspiring evildoers that they’ll do better down the block. And shooters tend to take that advice, attacking cafés, movie theaters, offices, elementary schools, and relatively unguarded streets rather than the fortified “targets” identified by consultants like, say, Rudolph Giuliani.

If President Trump really uses Trump Tower as his regular getaway from the burdens of the Oval Office, he will turn Fifth Avenue into an armed encampment. Trump himself may hardly notice the change just outside his door; after all, when he emerges from his black-and-gold bubble, it’s usually to slip into an idling car. But if he does ever go for a neighborhood stroll, he’ll find drivers skirting the area and clogging streets all around; retail business shriveling; and residents moving out. The rest of us will stay away and leave that section of sidewalk to the gawkers and the cops. The man in the high castle will have turned a public thoroughfare into a glowering moat.