“I have grave concerns as to whether Sergeant Bergdahl can receive a fair trial given the beating he has taken over many months from Mr. Trump, who will be commander in chief, as well as Senator McCain’s call for a hearing in case Sergeant Bergdahl is not punished,” Mr. Fidell said. “It is really most unfair.”

When Sergeant Bergdahl was released in May 2014, Mr. Obama appeared alongside his parents in the Rose Garden. The national security adviser, Susan E. Rice, said he had served with “honor and distinction.” His hometown in Idaho prepared a celebration. But the deal swiftly degenerated into a legal and political debacle.

The administration transferred the Taliban detainees without obeying a statute requiring it to notify Congress 30 days before the transfers. It said acting without delay was necessary to protect Sergeant Bergdahl’s life and argued that disregarding the statute in such circumstances was lawful, but Republicans maintained that the transfer was illegal.

In addition, former soldiers came forward to describe the circumstances of his capture, accusing him of desertion. That fueled Republican complaints that sending the Taliban detainees to Qatar had been too steep a price.

As furor swelled, the narrative about Sergeant Bergdahl further darkened. Some former soldiers alleged that he had been trying to join the Taliban and that five to seven Americans had died searching for him. Those allegations, however, proved false.

In June 2014, the secretary of defense at the time, Chuck Hagel, testified, “In all of our reports, I have seen no evidence that directly links any American combat death to the rescue or finding or search of Sergeant Bergdahl.” The military investigation also spotlighted the absence of such evidence.

Still, prosecutors have sought to introduce evidence in the trial that several soldiers were injured during the search. The defense has sought to block that evidence, arguing, among other things, that the real cause of the two most serious injuries prosecutors cited was botched planning for a particular raid. A judge has not yet ruled on that dispute.

The Army investigation concluded in 2015 that Sergeant Bergdahl had left his outpost intending to hike to another military post and report to an officer there on perceived wrongdoing involving his unit. A sanity board found that he had been suffering from a “severe mental disease or defect” at the time.