Tensions again flared on D.C. streets this week after groups of protesters erected barricades and set up tents and signs declaring an “autonomous zone” on city streets near the White House.

City officials mobilized Monday to clear out the area and returned Tuesday morning to remove similar signs.

President Trump tweeted Tuesday morning that attempts to form an “autonomous zone” would be met with “serious force,” which Twitter deemed a violation of the platform’s policies that prohibit threats of harm.

Here’s what you need to know about the developing situation.

What is the ‘Black House Autonomous Zone’?

It’s the term activists used to dub the area they cordoned off by setting up tents, an apparent contrast to the nearby White House and a homage to the “Capitol Hill Autonomous Zone,” an area of Seattle that police had withdrawn from in recent weeks.

“Black House Autonomous Zone” was painted in black on a piece of plywood near the barricades erected by activists. Another person tagged the initials “BHAZ” on the white pillars outside the historical St. John’s Episcopal Church.

This area has been at the heart of D.C. demonstrations. It’s directly north of Lafayette Square, where peaceful protesters were gassed by federal law enforcement earlier this month and where activists recently attempted to tear down a statue of former president Andrew Jackson. It is also where Mayor Muriel E. Bowser (D) ordered city crews to paint “Black Lives Matter” on the street in giant yellow letters.

But her administration quickly cracked down on attempts to turn the area into an encampment.

How did D.C. city officials respond?

City officials say they repeatedly warned people in tents to leave because it posed a danger to public safety before beginning to clear out the area Monday afternoon. Some tents remained on the sidewalk by the evening. Administration officials said they planned to reopen H Street NW to vehicular traffic.

Police Chief Peter Newsham said some demonstrators resisted, and two officers were assaulted. He said police arrested two people, and he acknowledged officers used pepper spray to move back the crowd.

Activists returned overnight, but so did D.C. police Tuesday morning. Around 10:30 a.m., officers closed off H Street from multiple access points and tore down newly installed signs and flags designating the area as the autonomous zone. By early Tuesday evening, no tents or signs were visible in the area, but protesters appeared to be ready to bring them back.

What are autonomous zones?

In Seattle, part of the Capitol Hill neighborhood received the “autonomous zone” moniker after protesters cordoned off the area when police vacated the precinct following a week of clashes with demonstrators. Activists demanded police officers stay away.

It became nationally watched and a target of ire by conservatives, who decried it as lawlessness and an example of Democrats being too willing to cave to demonstrators.

The occupants were mostly peaceful for two weeks, but police entered the area Saturday to respond to a shooting that left one man dead. Seattle Mayor Jenny Durkan (D) said police would return to the abandoned precinct in the “near future.”

Trump threatened ‘serious force’ if protesters set up an autonomous zone. What can he do?

Unlike in Seattle, Trump has more powers to intervene in the District of Columbia.

The city’s home rule charter allows the president to take over the local police department during emergencies — a step that has never been taken before and one that has been floated by the Trump administration in the early days of demonstrations, when unrest included looting and property damage across downtown. City officials have vowed to fight any attempt by the president to take over the police department.

The president also has considered invoking the 19th-century Insurrection Act to deploy active-duty military to quell unrest. The Pentagon had resisted the idea but in early June began moving forces to the Washington area in preparation for possible operations in the nation’s capital.

What has been the reaction to the city’s handling of the zone?

Bowser has basked in the national spotlight, with shout-outs from celebrities and appearances on late-night television and “The View” after her earlier confrontation with the president over demonstrations.

But activists have accused the mayor of being too deferential to police and allowing them to use heavy-handed tactics against demonstrators.

An emergency bill awaiting the mayor’s signature would prohibit police from using chemical irritants on protesters, as was the case when officers used pepper spray while breaking up the autonomous zone. But police have argued the prohibition would not apply if activists turned violent.