FORT BRAGG, N.C. 芒鈧珺次元官网网址� President Donald Trump's fiery criticism of Army Sgt. Bowe Bergdahl has put the desertion case against the soldier on uncertain ground as a judge considers whether he can still get a fair trial for walking off his post in Afghanistan in 2009.

The judge, Army Col. Jeffery Nance, called video of Trump repeatedly calling Bergdahl a traitor during campaign speeches "disturbing" at a pre-trial hearing Monday. He also asked prosecutors pointed questions about whether Trump's criticism has already created a public perception that Bergdahl won't be treated fairly.

Bergdahl's lawyers argue the comments violate their client's due-process rights and that the charges against him should be dismissed. The judge didn't immediately rule on the defence request, and a written decision was expected later.

In a video played in court, Trump promised his audience at a December 2015 campaign rally to review the case if Bergdahl got a light punishment.

Nance asked prosecutors: "You're not at all concerned about the statement he made, 'If I get in we will review his case' ... after ranting and raving about no jail time?"

Legal scholars have said that even if the judge agrees that Trump's comments crossed the line, he could try to salvage the case by giving defence attorneys wide leeway to question and dismiss potential military jurors.

Prosecutors say Trump's comments amounted to campaign rhetoric against actions taken by the Obama administration to bring Bergdahl home after he was held captive for five years by the Taliban and its allies.

"These comments are clearly intended to try to attack a political opponent for political gain," said Army Maj. Justin Oshana, a prosecutor.

The Obama administration's decision in May 2014 to exchange Bergdahl for five Taliban prisoners prompted some Republicans to accuse Obama of jeopardizing the nation's safety.

Oshana said potential jurors' exposure to Trump's comments could be addressed through questioning during jury selection.

But Nance asked, "How does that relate to overcoming the black eye to the military justice system ... the view the public might have?"

That question goes to the heart of the defence argument that Trump's comments constitute unlawful command influence by the new commander in chief. Even the appearance of such unfairness can theoretically derail a military case.

The defence's motion, filed shortly after Trump was sworn in as president, cites more than 40 instances of Trump's criticism at public appearances and media interviews through August 2016.

Eugene Fidell, Bergdahl's defence attorney, argued Monday that Trump has kept other campaign promises, so his comments about Bergdahl should be taken seriously.

A White House spokesman didn't respond to a phone call and email seeking comment Monday about whether Trump plans to review Bergdahl's case.

Bergdahl is charged with desertion and misbehaviour before the enemy, the latter of which carries a maximum penalty of life in prison. He has been assigned to desk duty at a Texas Army base while awaiting trial.

Bergdahl, who is from Idaho, has said he walked off his post to cause alarm and draw attention to what he saw as problems with his unit.

His trial is scheduled for April, but a delay seems likely after the judge set a new time frame for working out problems with the handover of classified information as part of the discovery process. He said he would give lawyers until the beginning of April to prepare a status report that will determine future dates in the case.

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Jonathan Drew, The Associated Press