Protests over Confederate symbols have erupted in several cities, following white nationalist violence in Charlottesville on Aug. 12. (Amber Ferguson/The Washington Post)

City officials across the country are nervously trying to figure out how to avoid becoming the next Charlottesville as alt-right leaders and white nationalist groups vow to stage more rallies in coming days.

A group claiming it is advocating free speech has planned a rally for Saturday on the historic Boston Common, with a group advocating racial justice planning its own gathering in opposition. Boston officials said they have laid down strict conditions, including no sticks, weapons or backpacks.

“Make no mistake: We do not welcome any hate groups to Boston, and we reject their message,” Mayor Marty Walsh (D) said Wednesday.

A rally scheduled for Aug. 26 in San Francisco has prompted House Minority Leader Nancy Pelosi (D) and several California lawmakers to urge the National Park Service to rescind the permit to gather on federal park land there.

Birmingham city workers use plywood panels to cover the Confederate Monument in Linn Park, in Birmingham, Ala., on Tuesday. (Joe Songer/AP)

Cities also are grappling with what to do about their Confederate monuments, an issue that has suddenly become much more urgent. Some are taking preemptive measures under the cover of night: Four Confederate monuments in Baltimore were hauled away in the early morning darkness Wednesday, and one in Birmingham, Ala., was covered in plywood.

In the wake of the violent public clashes in Charlottesville on Saturday, mayors, governors and other civic leaders are taking steps that even a week ago might not have seemed necessary. But they also are facing uncertain challenges, not knowing whether the white nationalist movement will attract a larger following or where the most turbulent demonstrations may occur.

Violence is at the center of the concerns, and the Charlottesville rally showed law enforcement authorities that they need to be better prepared.

Darrel Stephens, executive director of the Major Cities Chiefs Association, noted that many of the people who came to Charlottesville wore helmets and carried shields.

“These guys, the shields that they showed up with . . . you don’t bring that stuff to a demonstration to just express a view,” Stephens said. “You bring that there prepared for violence. Why else would you have them?”

Several Charlottesville residents reacted to the recent violence on Aug. 16, the day of Heather Heyer's memorial service. Heyer was killed on Aug. 12. while protesting white nationalists. (Dalton Bennett,Elyse Samuels/The Washington Post)

Richard Spencer, an alt-right leader, said Wednesday in a text to The Washington Post that his movement will return to Charlottesville, where Heather Heyer, 32, was killed and many people seriously injured when a driver plowed into a crowd of counterprotesters.

“This car accident or attack — we’re going to find out — was horrible, but the idea that it will destroy the identitarian movement is ridiculous,” Spencer said this week in a news conference at his office in Northern Virginia.

Identitarian is Spencer’s preferred term, however, most experts who study the alt-right consider it a growing wing of the white supremacist movement.

To head off potentially violent rallies, Baltimore Mayor Catherine E. Pugh (D) stayed up Tuesday night into Wednesday morning to observe contract workers hauling away four Confederate monuments. She said she told herself: “There’s enough grandstanding speeches being made. Get it done.”

Only an empty pedestal remained where the figures of Confederate Gens. Robert E. Lee and Thomas J. “Stonewall” Jackson had been astride their war horses. Also gone: statues honoring Confederate women, Confederate soldiers and sailors, and Supreme Court Chief Justice Roger B. Taney — the author of the 1857 pro-slavery Dred Scott decision saying African Americans could not be citizens.

Another statue of Taney is in Annapolis, on the grounds of the State House, and Maryland Gov. Larry Hogan (R) has reversed course and decided he wants it removed.

“While we cannot hide from our history — nor should we — the time has come to make clear the difference between properly acknowledging our past and glorifying the darkest chapters of our history,” Hogan said.

In Richmond, once the capital of the Confederacy, Mayor Levar Stoney (D) announced a dramatic change of heart about the statues lining Monument Avenue. He had favored adding interpretive material to put the Confederate statues in context. But he said Charlottesville’s violence led him to a new conclusion — that the statues must go.

“While we had hoped to use this process to educate Virginians about the history behind these monuments, the events of the last week may have fundamentally changed our ability to do so by revealing their power to serve as a rallying point for division and intolerance and violence,” Stoney said in a statement. “These monuments should be part of our dark past and not of our bright future. I personally believe they are offensive and need to be removed.”

Cities are worried that they could become flash points for public actions they have taken on behalf of their citizens. A working group of the Lexington-Fayette Urban County Council in Kentucky voted unanimously on Tuesday to move Confederate statues from their locations at the old county courthouse. The full council will vote on the measure Thursday, where it is expected to pass, Mayor Jim Gray said. If it does, the city will have to seek approval of the state Military Heritage Commission.

The city’s attempt to move, rather than remove, Confederate monuments has not appeased white supremacists. Matthew Heimbach, chairman of the Traditionalist Worker Party — a white supremacist group — told the Lexington Herald-Leader that the organization is planning a rally there “sooner rather than later.” Lexington police are conferring with federal officials to prepare.

In Birmingham, Ala., city officials covered a Confederate monument in a city park with plywood and tarps while lawyers studied the city’s options, as Alabama state law penalizes cities with a $25,000 fine if they violate a prohibition against removing monuments.

Mayor William Bell (D) said the city has been looking into removing the monument for two years. The Unite the Right rally in Charlottesville made him worry, he said, that the monument would be “a lightning rod for organizations and individuals preaching hatred.” But the city is facing legal action from Alabama Attorney General Steve Marshall, who said that hiding the statue from public view“altered” or “otherwise disturbed” the memorial “in violation of the letter and spirit” of the law, leaving him no choice but to sue.

Bell said he believes he will succeed in removal, but if not, he hopes the city can place markers nearby that describe the horrors of slavery. “There are two forces at work here: Whether or not we will continue to glorify an action that sought to end these United States of America as we know it today, and whether or not the state has the right to protect monuments that really speak to the suppression of human beings,” Bell said.

Colleges have been resisting attempts to have rallies on their campuses, and in the days after the Charlottesville violence, schools including Texas A&M and the University of Florida canceled events tied to white nationalist groups that were scheduled for the week of Sept. 11. In Gainesville, officials were alarmed about the possible alt-right rally, which has been referenced on social media: “The Next Battlefield is in Florida.”

University of Florida President W. Kent Fuchs cited safety concerns in canceling the event. On Facebook, he wrote that the university remains dedicated to free speech and public discourse but added, “the First Amendment does not require a public institution to risk imminent violence to students and others.”

The Charlottesville violence also led to the cancellation of protests that had been planned for Saturday outside Google offices throughout the country, a response to the recent firing of a Google employee who had questioned diversity efforts. But on Tuesday, the organizers canceled the rallies, claiming endangerment from “left-wing terrorists.”

Louisville Mayor Greg Fischer (D) directed the Louisville Commission on Public Art to develop a list of works that “can be interpreted to be honoring bigotry, racism and/or slavery,” so he can consider whether to add more art, move some of them around or add markers to better explain the artworks.

“The situation is complicated, and we need to meet that challenge,” Fischer said. “And anyone who wants to engage in peaceful conversation is welcome to the table. Anyone who wants to engage in violence or hate speech is not.”

Some cities want the Confederate monuments discarded by other cities. That’s the case in Brandenburg, Ky., which took a monument removed from the campus of the University of Louisville and dedicated it on Memorial Day.

“We had a lot of support, and so far we haven’t had any trouble,” said Tammy Weick, the treasurer of Meade County, which has partial responsibility for maintaining the monument. “We’re not taking it down; it’s here to stay.”

In North Carolina, protesters toppled a bronze Confederate soldier statue that stood in front of a county administration building in downtown Durham on Monday. And Gov. Roy Cooper (D) demanded that the state legislature repeal a law preventing the removal of monuments, citing Saturday’s violence: “It started with a monument, stone and metal, inanimate and yet more provocative now than ever. Charlottesville could have been Raleigh, or Asheboro, or any other city in North Carolina that is home to a Confederate monument.”

Elizabeth Dwoskin, Fenit Nirappil, Emma Ockerman, Sarah Larimer, Michael Miller and Ovetta Wiggins contributed to this report.