A lawsuit accusing the publisher of the neo-Nazi site Daily Stormer of coordinating a “terror campaign” of online harassment against a Jewish real estate agent cannot be dismissed on First Amendment grounds, a federal judge in Montana ruled this week.

In his ruling denying a motion to dismiss the lawsuit, Dana L. Christensen, the chief judge for United States District Court in Missoula, Mont., wrote that the real estate agent, Tanya Gersh, was a private citizen, not a public figure, and that the publisher, Andrew Anglin, incited his followers to harass her as part of a personal campaign.

The events that spurred the lawsuit began in the fall of 2016, when The Daily Stormer published a series of articles attacking Ms. Gersh, of Whitefish, Mont., for her interactions with Sherry Spencer, the mother of the white supremacist leader Richard Spencer.

Ms. Spencer owned a building in Whitefish and Ms. Gersh had talked to her about its potential sale after word circulated that residents were considering a protest there against white supremacy.

The call to protest was spurred by video of Mr. Spencer, who resided part time in Whitefish, railing against Jews and shouting “Hail Trump! Hail our people!” at an alt-right meeting in Washington, according to the suit.

The suit contends that Ms. Gersh counseled Ms. Spencer to sell the building and repudiate her son’s views. And initially, Ms. Spencer agreed, it says, even asking Ms. Gersh to represent her in such a sale.

Then Ms. Spencer reversed course, and published a blog post on Medium, charging that Ms. Gersh had tried to threaten and extort her to sell the building and break with her son. Mr. Anglin then began writing and publishing his own articles calling for “a troll storm” against Ms. Gersh.

“Tell them you are sickened by their Jew agenda to attack and harm the mother of someone whom they disagree with,” he wrote, according to the suit.

In the months that followed, the site published over 30 related posts — and the phone numbers, email addresses and social media profiles of Ms. Gersh, her husband and 12-year-old son, as well as friends and colleagues, the suit states.

By the spring of 2017, the family had received more than 700 vulgar and hateful messages, including death threats, many referencing the Holocaust. Some phone messages consisted solely of the sound of gunshots.

The Southern Poverty Law Center filed the lawsuit on Ms. Gersh’s behalf in April 2017. Mr. Anglin sought to have it dismissed, and a magistrate judge, Jeremiah C. Lynch, ruled against him in May. Mr. Anglin filed objections to that ruling, which sent the case to Judge Christensen for additional review.

David Dinielli, a lawyer for the law center, said in a statement that Judge Christensen’s ruling on Wednesday “underscores what both we and our client have said from the beginning of this case — that online campaigns of hate, threats, and intimidation have no place in a civil society, and enjoy no protection under our Constitution.”

In a phone interview, Mr. Dinielli said that the Gersh family had notified law enforcement of the harassment, but there have been no criminal charges.

The organization now expects the civil case to go to trial. It has taken a long time because it proved impossible to serve Mr. Anglin with legal papers, Mr. Dinielli said. Mr. Anglin’s last known address was in Ohio, but his whereabouts have been unknown for nearly two years. He is still running the site, possibly from overseas.

His lawyer, Marc Randazza, said that Judge Christensen’s decision was dangerous for free speech.

“The rule we lay down for the Nazi applies equally to the civil rights activist,” Mr. Randazza said in a statement. “And that ruling, if it stands, is not going to be good for anyone who engages in common outrage culture. Maybe that’s a good thing, but I think not.”

The site has also faced two other lawsuits. Taylor Dumpson, the first black woman to serve as American University’s student government president, filed a suit in May. She became an online target after a real-life incident: nooses and hateful messages left on campus a day after her inauguration. The suit was filed by the Lawyers’ Committee for Civil Rights Under Law.

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Dean Obeidallah, a Muslim comedian and radio host, filed a defamation lawsuit in August 2017 after the site falsely accused him of masterminding the deadly bombing of an Ariana Grande concert in Manchester, England, last year.

Mr. Anglin never responded, and Mr. Obeidallah said his lawyers were preparing to file paperwork for a default judgment.

“I don’t expect us to collect any money,” he said by email. “But if we did collect any money from Anglin I would donate it all to organizations that fight bigotry and racism.”

The site was booted from Google and GoDaddy web hosting services after it posted an article mocking Heather D. Heyer, the woman killed in an attack on counterprotesters at a white nationalist rally in Charlottesville, Va., last year.

It then bounced around the globe with different web domains, and is currently online with the domain name “.name.” There have also been reports that Mr. Anglin is using crypto-currency to fund the site.

“He should be assured that if we end up with a judgment, we will go to the ends of the earth to collect, so that he doesn’t do this again and can no longer publish,” Mr. Dinielli said.