The mayor added: “When they come to City Hall to protest — even though I don’t like what they say all the time — we don’t say: ‘Nope, sorry, you’ve got to be over by the river.’ It’s an American tradition. It’s a good one.”

On Thursday morning, vehicles flowed down Fifth Avenue (as much as they can ever be said to flow down Fifth Avenue). But the east sidewalk was closed between 56th and 57th Streets. That isolated the main entrance of Tiffany & Company, under the nine-foot Atlas clock.

Tiffany’s is open for business and keeping regular hours, a spokesman for the store said. Customers can use the 57th Street entrance. On Thursday, at least, they were also able to exit through the Fifth Avenue doors, though some looked disoriented to find almost no one else on the normally bustling sidewalk outside.

The Atrium at Trump Tower — home of the Trump Bar, the Trump Grill, Trump Cafe, Trump’s Ice Cream Parlor, the Trump Store and Trump Events — is also open to the public. But on Thursday, it took some determination even to get there. Obliging police officers let a few pedestrians past the 57th Street checkpoint.

Though the sidewalk on the west side of Fifth Avenue was open, it felt like a cattle chute. An impromptu press pen squeezed passers-by. Construction hoardings worsened the choke point. Even on a beautiful day in late autumn, tempers seemed to be set at mid-August levels, as impatient New Yorkers tried to squeeze past selfie-snapping tourists.