Just days before he takes on former Milwaukee County Sheriff David A. Clarke Jr. in federal court, the plaintiff who says Clarke infringed on his free speech rights after an airport encounter has lost his lawyer.

William F. Sulton has represented Dan Black since he sued Clarke in February, claiming several violations of his civil rights. Earlier this month, the judge dismissed most of Black's claims but said a jury should decide whether Clarke retaliated on social media against Black for criticizing the then-sheriff.

The trial is set for Monday and is expected to last just one day. On Wednesday, Sulton withdrew from the case, citing the conflict created when his law firm, Peterson, Johnson & Murray, merged Jan. 2 with von Briesen & Roper, which counts among its clients Milwaukee County. Another large firm, Husch Blackwell, represents Clarke in this case.

"It is with great regret that I file this motion," Sulton wrote. "But I must."

According to Sulton, even though the county is no longer a party to the lawsuit, it would have to pay any judgment awarded Black by the jury. He said there was some talk the county would waive the conflict.

" I am now being told that it will not. And so I must withdraw."

But Sulton said the trial need not be delayed because his mother, Anne T. Sulton, would take over Black's representation.

Anne Sulton said she retired from a national civil rights practice in 2015 but was happy to take over Black's case at the last minute for her son.

"I don' think the county knew his mama's a civil rights lawyer, too," she said.

Sulton spoke by phone Friday from her home in the Seattle area. She graduated from the University of Wisconsin Law School in 1985 and maintains a state law license. She also has a Ph.D. in criminology.

"I think this will be the most important trial happening in America next week," she said. "The First Amendment is critically important, and we set the standard for free speech around the world."

Black and Clarke were on the same flight from Dallas to Milwaukee on Jan. 15, 2017. Black saw Clarke wearing Dallas Cowboys gear and asked if he was David Clarke. Clarke said he was, and Black shook his head and walked away to his seat in coach.

When the plane landed in Milwaukee, Black was greeted by six sheriff's deputies who had been directed by Clarke to take Black aside and question him, which two of them did. They then escorted him from the airport.

Black later posted on social media about the incident and filed a complaint with the county. Clarke responded on social media by calling Black "Snowflake."

Clarke's lawyers have asked U.S. District Judge J.P. Stadtmueller to read a short summary of Black's encounter with Clarke on the airplane and his interaction with deputies when the plane landed in Milwaukee.

The statement would then instruct the jury "that the conduct of both Clarke and Black in the airplane and at the airport was proper and did not violate the law. This lawsuit is solely about events after Black left the airport involving Facebook posts."

Clarke also asked that potential jurors be given a questionnaire in advance that asked the usual questions about residence, education, employment and prior jury service, but also their general opinion of Clarke and which social media and news outlets they use, and how concerned they are about abuse of police power, free speech, racism and freedom from unreasonable search and seizure.

Stadtmueller denied the request, saying the usual jury selection process in court would suffice.

The only issue left for the jury to decide is whether Clarke's posts about Black, on the Sheriff's Office official Facebook page, in the wake of the airport incident, amounted to retaliation against Black for filing a complaint about Clarke with the county over the airport incident.

Black contends Clarke harassed and threatened him via posts on Facebook.

Someone claiming First Amendment retaliation usually must show he was subjected to a campaign of petty harassment, a threat of physical harm or of some kind of punishment, sanction or adverse regulatory action.

"In contrast, an isolated instance of public ridicule will not amount to actionable retaliatory harassment unless it is egregious enough to deter a person of ordinary firmness from exercising his right of free speech," Stadtmueller wrote in a Jan. 5 order narrowing the issues for trial.

He cited a state appeals court ruling in a different case involving Clarke. On a call to a radio talk show, he responded to a deputy's criticism by calling the deputy "a slacker" who was bitter about being disciplined for sexual harassment. That court found the on-air comments did not amount to First Amendment retaliation.

"After all, the Court must take into account the defendant speaker's own right to free speech," Stadtmueller wrote.

Clarke's attorneys say the key question is whether Clarke's posts would "chill a person of ordinary firmness from continuing to engage in the protected activity."