In this photo provided by attorney Eugene R. Fidell, Sgt. Bowe Bergdahl prepares to be interviewed by Army investigators in August 2014.

The attorney for Bowe Bergdahl, the Army sergeant accused of deserting his base in Afghanistan before he was taken prisoner by the Taliban, says presidential candidate Donald Trump’s criticism of his client threatens Bergdahl’s ability to get a fair trial.

In a statement released Thursday, attorney Eugene Fidell said Trump’s derision of Bergdahl as a “dirty, rotten traitor” was “contemptible and un-American” and threatened to color the opinions of jurors in a potential court-martial.

“Sergeant Bergdahl is not charged with treason or anything like it,” Fidell said, condemning “Mr. Trump’s reckless disregard for the truth.”

Bergdahl, who is charged with desertion and misbehavior before the enemy, faces an investigative hearing in September, which will decide whether his case should be referred to trial.

Bergdahl was released by Taliban fighters last year in a controversial prisoner swap that included the release of five Taliban militants held in the military prison at Guantanamo Bay, Cuba. He was captured in 2009 after he abruptly left his base.

Soldiers in Bergdahl’s unit said he had no plans to return. Fidell has said Bergdahl was trying to draw attention to problems inside the base.

Bergdahl’s attorneys have repeatedly questioned his ability to get a fair trial, several times comparing public attitude toward the soldier to a lynch mob.

Trump lashed out against Bergdahl during the recent Republican debate. At a town hall in New Hampshire this week, he also claimed that U.S. servicemembers died while searching for Bergdahl. Fidell said the candidate was “misinformed.”

“Mr. Trump’s comments, along with many others that have been made over the last year, directly threaten my client’s right to a fair trial,” Fidell said.

“Mr. Trump must stop vilifying this young man, who suffered five years of brutal captivity at the hands of the Taliban and deserves to be judged on the basis of evidence rather than slander from someone who has never worn our country’s uniform,” Fidell wrote.

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