Policing and prosecuting local white supremacy? There’s one major legal hurdle that makes it difficult.

Marchers bearing the insignia of the white supremacist group Patriot Front paraded through Boston on July 2.Michael Dwyer/Associated Press

About 100 members of the white supremacist group Patriot Front had just marched through Boston — roughing up a Black man along the way — when a State Police helicopter spotted the group’s U-Haul truck driving north on Interstate 93. The truck was stuffed with the riot shields members had marched behind, stirring outrage.

But transporting riot shields is not illegal. Instead, after police pulled the truck over, they gave the driver, 23-year-old Colton M. Brown of Ravensdale, Wash., a criminal citation for illegally attaching a plate to the vehicle. The maximum penalty? Ten days in jail.

Despite the outcry over the growing visibility of right-wing extremists in the Northeast, police have limited options for charging them criminally. On the few occasions they have brought charges, it’s been for minor offenses and almost none have faced meaningful consequences.

A Boston Globe review of 11 men in the region who faced criminal charges related to white supremacist activity over the last three years — mostly related to vandalism — shows most charges were later dropped.

None of the white supremacists served time in jail and only a few paid a financial price. Brian D. Harwood had to pay $1,197 restitution to the town of Dennis for his role in white supremacist graffiti appearing on basketball courts, a bicycle trail, and a beach, court records show. Zachary Pickering was ordered to pay $250 to the NAACP for vandalizing public places in Rhode Island.

The challenge, say legal scholars, is simple, albeit maddening for those who want a more muscular response against groups that openly preach hate against people of color, Jews, gay people, and others. The First Amendment casts a wide legal net, they point out, protecting offensive speech from law enforcement.

“Hate is as American as apple pie,” said Harvey Silverglate, a Cambridge criminal defense and civil liberties attorney. And, as far as the Constitution is concerned, “Hate speech has the same legal standard as love speech.”

Police in the United States are not supposed to police ideology, and the repugnance of offensive speech, such as Nazi symbols or overtly racist rhetoric, is not relevant to whether it’s protected under the Constitution, said David Siegel, a professor at New England Law | Boston.

What is not protected is inciting violence, which could mean gathering a large group of people with the intent of attacking someone or saying things to other people that are so offensive they present an imminent breach of the peace, said Siegel.

”So-called fighting words,” said Siegel.

That means the police were limited in what they could do on July 2 when scores of Patriot Front activists marched through the city. While a scuffle did break out between a Black activist and the white nationalists during their march, no charges have been filed related to that incident.

If the march had crossed onto private property, individuals might have been charged with trespassing. That’s what happened earlier this summer in East Providence, R.I., when Neo-Nazis who were stapling fliers on poles allegedly entered the grounds of a private elementary school. But in the Boston case, marchers appeared to stick to public roads, sidewalks, and parks.

Mayor Michelle Wu has said the chief difference between the July 2 march in Boston and a recent incident in Idaho where authorities arrested 31 members of Patriot Front was that in the Idaho incident, there was law enforcement intelligence that the group was there to disrupt a Pride event and possibly cause violence. The men were charged with conspiracy to riot, a misdemeanor.

In Boston, police have maintained they did not have prior knowledge of the march through the city.

But critics have lambasted law enforcement for that failure of intelligence. Brown, for instance, has been on the radar of law enforcement across the country. In June, he was among the 31 Patriot Front members arrested near the Pride event in Coeur d’Alene, Idaho. Reached by the phone, Brown declined to comment. “I don’t talk to journalists. Have a good day,” he said.

Limits on police power to shut down demonstrations, despite vehement opposition to the events’ central message, is not a new problem for Boston. Former mayor Martin J. Walsh’s administration was under pressure to nix events such as the Straight Pride Parade in 2019 or a “free speech rally,” which authorities worried would attract white supremacists, in 2017. Both events received permits because Walsh’s office did not have legal grounds to deny them. (The July 2 white supremacist march did not have a permit, which Boston police have said is not uncommon for protests.)

Wu addressed the recent rash of white supremacist activity locally in an appearance on GBH in late July, saying Boston police have “ramped up” a force in the department “that are basically ready to go when we know that there are many events scheduled across the city, they can immediately show up and have a zero tolerance policy.”

“That means whenever any line is crossed that is beyond the First Amendment,” she said, exposing demonstrators to charges such as disturbing the peace or vandalism.

Wu did acknowledge that prosecutors sometimes struggle to secure convictions, adding, “But it is our obligation to make it difficult.”

Indeed, when charges do come for local white supremacists, they are often for relatively minor offenses, and, in many instances, they don’t stick.

Take Harwood, a 24-year-old Spencer resident who court documents identify as a leader of the white supremacist Patriot Front’s New England division; Brown told State Police he rented the U-Haul used by Patriot Front members during the July 2 Boston demonstration.

Harwood has been criminally charged in three different towns related to his activities with Patriot Front, but, so far, he has only paid restitution for property damage once and has no criminal record.

Currently, he is being prosecuted in Framingham District Court for vandalizing property and conspiracy over allegations that he directed a member of the organization to put Patriot Front stickers on property on the campus of Framingham State University. He has pleaded not guilty to charges of conspiracy and vandalism.

Two years ago, Dennis police arrested Harwood after tracking Patriot Front graffiti on public property back to him. Police got a warrant for data from Harwood’s cellphone and recovered text messages, location information, and videos that implicated him in the vandalism. “Twas awesome,” Harwood texted.

Harwood was ordered to pay $1,197 in restitution in the Dennis case and complete 20 hours of community service in the Yarmouth case, but ultimately all the criminal charges against him were dropped, court records show.

Reached by phone, Harwood hung up on a reporter.

Other times, police investigating extremists have found little evidence to support criminal charges.

Haverhill police were investigating reports of a Patriot Front activist flashing a gun when they searched the home of 19-year-old Justin Milaszewski last July. But they only found a BB gun, stickers, and a flag bearing the symbol of a white supremacy group.

“One sticker and now I’m Hitler,” Milaszewski told his sister during the search, according to a police report. Police filed several charges, including defacing property and assault with a dangerous weapon, against Milaszewski, but all were thrown out after a judge approved a defense motion to dismiss the case, court records show.

Milaszewski couldn’t be reached for comment. His sister threatened the Globe with legal action if it wrote about the case.

The only man accused of white supremacist activity to admit to a criminal charge locally is Tylar Larson, 22, of Rochester, N.Y., who was carrying a set of black brass knuckles and a wood handled trowel when police pat frisked him in East Boston’s Maverick Square on Feb. 15, 2019. He was part of a group dressed in hoods and face masks and carrying stencils of slogans for Patriot Front.

Larson admitted to sufficient facts a month later, court records show, and was placed on unsupervised probation for six months.

This past weekend, Neo-Nazi group Nationalist Social Club 131 again descended on Boston, this time on Sunday outside a drag queen story hour event in the Seaport. The featured performer canceled the event and no arrests were reported.

Lawyers say it’s not surprising the white supremacists are largely escaping legal punishments in a nation that values freedom of speech. Siegel, the New England Law professor, said white supremacy represents “a deep problem that street-level arrests for disorderly conduct or breach of the peace . . . doesn’t address and can’t address.”

Daniel Medwed, a law professor at Northeastern University, said law enforcement should intervene in demonstrations only if the event poses a “clear and present danger,” meaning the risk of a riot, for instance, or obstruction of traffic that threatens public safety.

“So, the devil is really in the details here,” he said.

Travis Andersen and Amanda Milkovits of the Globe staff contributed to this report.