A federal drug trial unfairly included inflammatory evidence that the defendant was a member of the Mexican Mafia at a time when then-presidential candidate Donald Trump was calling Mexicans "rapists'' and his supporters were shouting, "Build the wall,'' the man's lawyer argued in court Tuesday.

A government lawyer countered that the gang information helped jurors understand the relationship between the men accused of methamphetamine distribution and established defendant Fulgencio Arias Jr.'s motive.

The arguments before a federal appeals panel in Portland raised a timely question in today's polarized political climate about the impact of gang designations on juries.

Even if it was a mistake to identify Arias' gang ties during trial, it didn't harm him because the drug trafficking evidence against him was overwhelming, said Finnuala K. Tessier, an appellate attorney for the U.S. Department of Justice.

Judge Andrew D. Hurwitz of the 9th U.S. Circuit Court of Appeals interjected, asking why the gang information was necessary then.

"At some point doesn't the government have some obligation to temper what it puts in the case like this, recognizing how prejudicial gang affiliations can be?'' Hurwitz said. "Does the Mexican Mafia have to be mentioned?''

"The government is allowed to put on a strong case,'' Tessier responded.

"But not to go so far as to make the trial prejudicial,'' Hurwitz said.

He added: "My concern, in general, is I see very strong cases in which the government adds on gang evidence, and I wonder if that's a wise thing. I say this as a matter of caution, and I hope your colleagues hear it, too.''

Arias was convicted of conspiracy to distribute methamphetamine, distribution of methamphetamine and money laundering after a trial in May 2016 and sentenced to 25 years in prison. Prosecutors said he ran a large-scale drug-trafficking trade in Oregon, Washington and Montana and laundered the drug proceeds through cash deposits in co-conspirators' bank accounts.

A co-defendant testified that he knew Arias to be a member of the street gang Arizona Maravilla and that he knew Arias would do the "grimy work" for the Mexican Mafia, according to a government filing.

The Mexican Mafia is a California-based prison gang that was founded in 1956 when several dozen convicts conspired to take control of drugs, gambling and prostitution. Law enforcement officials say members are known to use intimidation, extortion and murder to control much of the region's criminal activity, particularly drug sales by street gangs.

Attorney Laura Graser, who filed the appeal on Arias' behalf, argued that the gang evidence was irrelevant to the government's case.

"This is extraneous race-based character assassination,'' she said.

Hurwitz asked why the prejudicial impact was so great.

Graser pointed to one of the gang's symbol, the black hand of death, and its reputation for assault and murder.

She also cited "the political climate that summer where crowds were chanting, 'Build the wall! Build the wall!' and the leading presidential contender was saying that the Mexicans here were rapists.''

In her legal brief, Graser noted that the timing of the May 2016 trial was "particularly unfortunate'' as it was held 11 months after the "ultimately successful candidate for president of the United States made his campaign announcement with his well-known characterizations of Mexicans.''

Social science studies say "that gang evidence overwhelms a jury,'' Graser added. She submitted articles on the prejudicial impact of gang evidence on jurors, including one in 2013 that ran in the Journal of Forensic Psychology Practice.

"So I'm supposed to go along with this social study rather than go along with tactics judges have used to avoid bias for centuries?'' Judge N. Randy Smith asked.

"There's a time when jury instructions can't unring the bell,'' Graser said.

Tessier argued that the trial judge, U.S. District Judge Marco A. Hernandez of Portland, engaged in a careful balancing act and took steps to minimize prejudice. He offered to question potential jurors if they held any anti-gang biases, limited evidence of violent conduct by the Mexican Mafia and instructed jurors before their deliberations not to use the gang ties, which might suggest a bad character trait, to conclude a defendant committed an offense.

Tessier said the gang affiliation was "inextricably intertwined'' with the charges Arias faced -- he met a co-defendant through their mutual Mexican Mafia connections while previously in custody in federal prison in Sheridan.

The jury is allowed to hear a "coherent and comprehensible'' story regarding the crime and not make its decision in a void, without knowledge of the full circumstances, she said.

The three-judge panel now will take the appeal under advisement and issue a ruling at some point in the future. Past court rulings on this issue have rested on the purpose for which a gang link is introduced into evidence and whether its admission was unfairly prejudicial. If the court sides with the defendant, a new trial likely would be held.

-- Maxine Bernstein

mbernstein@oregonian.com

503-221-8212

@maxoregonian