WASHINGTON — President Trump was furious when news got out last weekend that as protesters gathered outside the White House he had been rushed to an underground bunker. But now, as crowds keep coming back to demonstrate, the entire White House seems to be turning into one.

Every day, more fences go up and more concrete barriers are put in place as the security perimeter expands farther and farther. The universally recognized symbol of American democracy increasingly looks like a fortress under siege in the heart of the nation’s capital, a Washington version of the Green Zone that sheltered American and Iraqi officials in Baghdad during the worst of the war.

The measures taken over the last week have made the compound occupied by the president, his family and his staff more sealed off from demonstrations but also more removed from the American public. National Guard troops and riot police will certainly withdraw at some point, and White House officials say the barriers will be eventually removed. But history shows that security changes made at the White House in the heat of a momentary perceived threat often become lasting fixtures.

With the capital awash in security forces and much of downtown boarded up, Washington officials bristle at the martial moment and fear that the city is being transformed once more in a way evoking locked-down authoritarian nations instead of an open, pluralistic society.

“Keep in mind that that’s the people’s house,” Mayor Muriel E. Bowser said this week even as she sent Mr. Trump a letter asking him to withdraw extra security forces from the streets. “It’s a sad commentary that the house and its inhabitants have to be walled off.”

Ms. Bowser sent a signal of her own overnight, dispatching city workers on Friday to paint the words “Black Lives Matter” in giant yellow letters covering the entirety of two blocks of 16th Street leading toward the White House. She also posted a sign renaming the area Black Lives Matter Plaza.

White House officials stressed that the changes were not ordered by Mr. Trump but were made at the direction of the Secret Service based on its assessment of the security situation. Small fires were set as close as a block away from the compound last weekend, including one that did minor damage at the iconic St. John’s Church, and a few protesters penetrated a barricade near the Treasury Department, next door to the White House. The authorities said dozens of law enforcement personnel had been injured in scrapes with protesters.

But while the demonstrations near the White House have been predominantly peaceful, especially as the week has progressed, Mr. Trump shows no discomfort with the increasing security. He has embraced the idea of military units in the streets of the capital, seeing it as a demonstration of strength and berating governors for not using the National Guard more in their states.

“They came in, and this was like a piece of cake,” Mr. Trump said at a news conference at the White House, sheltered behind the new fencing and surrounded by security. “Call in the National Guard. Call me. We will have so many people, more people then you have to dominate the streets. You can’t let what’s happened happen. It’s called dominate the streets.”

The Secret Service said on Friday that it was closing off the areas beyond the 18-acre White House compound until June 10 but did not explicitly say whether the barriers would then come down. “These closures are in an effort to maintain the necessary security measures surrounding the White House complex, while also allowing for peaceful demonstration,” it said in a statement.

With the demonstrations still ongoing, the White House was bracing for the possibility of hundreds of thousands of protesters descending on Washington on Saturday. The White House declined to discuss the matter on the record. “The White House does not comment on security protocols and decisions,” said Judd Deere, a spokesman.

But another official, speaking on condition of anonymity to discuss security protocols, said there was no intention to make the new fencing and concrete barriers permanent and compared the expanded perimeter to the temporary measures taken when Pope Francis visited President Barack Obama in 2015.

For now, at least, the images are jarring. “The White House is the people’s house,” said Lindsay Chervinsky, a presidential historian at the Institute for Thomas Paine Studies at Iona College. “The American people own it, pay for it and permit the president to live there. The fencing and barriers show that Trump is rejecting his predecessors’ example and instead concealing himself from the American people.”

Plenty of critics and commentators compared the additional barriers around the White House to the wall he is building along the nation’s southern border, a small-scale manifestation of his desire to wall off outsiders. In this case, the outsiders are not foreigners but fellow Americans.

“If Trump erected more than three miles of fence around the White House, it would exceed the length of his new wall on the southern border,” Anthony Scaramucci, who served briefly as Mr. Trump’s White House communications director before breaking with him, wrote on Twitter. “His bigotry is only exceeded by his incompetence.”

For now, at least, the new security perimeter has annexed Lafayette Square, a leafy landmark with its signature statue of Andrew Jackson on horseback just north of the White House, where for a couple hundred years city residents, tourists, protesters and cranks have strolled, shouted and speechified.

A new chain-link fence about eight feet tall was first erected this week along the park’s northern edge, forcing the demonstrations farther away from the White House. The fencing has now been extended down 17th Street, along the western side of the White House compound, and about halfway along Constitution Avenue, the southern border of the Ellipse. Concrete barriers have been put behind the fencing in many places. Stacks of fencing segments were piled on 15th Street on Friday for workers to complete the perimeter.

The barriers reflect a radical evolution since the early days of the mansion. Thomas Jefferson, the first president to live eight years in the building, installed a low, wooden and rail fence and later a stone wall, but the grounds were kept open to the public. In 1833, according to the White House Historical Association, the stone wall was cut down and a heavy wrought-iron fence was installed along Pennsylvania Avenue. Ulysses S. Grant expanded the grounds and the iron fencing.

For generations, the public largely had the run of the grounds during daytime, treating it as an open park of sorts. Jackson invited thousands into the mansion itself on his Inauguration Day, a moment of populist mayhem that served as a metaphor for his presidency.

Irritated that visitors were trying to photograph his daughter, Grover Cleveland closed the South Grounds in 1893, and William Howard Taft restricted the North Grounds to certain days in 1913. Still, outsiders managed to wander in from time to time, including one who slipped into the building and watched a movie in the dark with an unsuspecting Franklin D. Roosevelt.

The grounds were closed altogether to the public during World War I and World War II, and the first version of the bunker that Mr. Trump would later be taken to was built under Roosevelt in case of enemy attack. In addition, soldiers camped on the grounds and gun crews were stationed on the roof. But Roosevelt rejected deploying tanks outside the mansion “because it might look as if our democracy was under siege,” as the historian Michael Beschloss noted.

Protests were permitted along Pennsylvania Avenue and in Lafayette Square during the Vietnam War, close enough that Lyndon B. Johnson could hear them chanting, “Hey, hey, L.B.J., how many kids did you kill today?” But in 1995, after a drunken pilot crashed a Cessna 150L onto the South Lawn, a gunman opened fire at the White House from outside the gates and militia members blew up a federal building in Oklahoma City with a truck bomb, Bill Clinton closed Pennsylvania Avenue to vehicle traffic.

The street was further closed to pedestrian traffic for three years after the attacks of Sept. 11, 2001, and the bunker under the White House where George W. Bush was brought during subsequent terror scares has since been upgraded. After intruders made it onto the grounds during Mr. Obama’s presidency, the government designed a more formidable 13-foot steel fence with what the police called “anticlimb and intrusion detection technology” to replace the historic one about half as tall.

As it happens, construction on that new fence began only last year and is not scheduled to be completed until next year.