Military prosecutors have reached into a section of military law seldom used since World War II in the politically fraught case against U.S. Army Sgt. Bowe Bergdahl, the soldier held prisoner for years by the Taliban after leaving his post in Afghanistan.

Observers wondered for months if Bergdahl would be charged with desertion after the deal brokered by the U.S. to bring him home. He was -- as well as misbehavior before the enemy, a much rarer offense that carries a stiffer potential penalty in this case.

Bergdahl could face a life sentence if convicted of the charge, which accuses him of endangering fellow soldiers when he "left without authority; and wrongfully caused search and recovery operations."

Observers say the misbehavior charge allows authorities to allege that Bergdahl not only left his unit with one less soldier, but that his deliberate action put soldiers who searched for him in harm's way. The Pentagon has said there is no evidence anyone died searching for Bergdahl.

"You're able to say that what he did had a particular impact or put particular people at risk. It is less generic than just quitting," said Lawrence Morris, a retired Army colonel who served as the branch's top prosecutor and top public defender.

The Obama administration has been criticized both for agreeing to release five Taliban operatives from the Guantanamo Bay prison and for heralding Bergdahl's return to the U.S. with an announcement in the White House Rose Garden. The administration stood by the way it secured his release even after the charges were announced.

The military has scheduled an initial court appearance hearing for Bergdahl on Sept. 17 at Fort Sam Houston, Texas. Afterward the case could be referred to a court-martial and go to trial.