That exchange, captured on a cellphone and uploaded to YouTube, has led Coombs to request Obama's presence at Fort Meade "in order to discuss the issue of unlawful command influence."

The Uniform Code of Military Justice prohibits a superior officer in the chain of command from comments or actions that could influence the deliberations of a subordinate charged with handling a military justice matter. As president, Obama is the commander-in-chief of U.S. armed forces.

"I will bet my copy of the Manual for Court-Martial that neither President Obama nor Secretary Clinton nor Secretary Gates ever testifies in this case," said Fidell, a co-founder and former president of the National Institute of Military Justice. "I find it hard to believe that any investigating officer, or thereafter, any military judge, assuming this case goes to trial, would see them as critical to the development of the case or to the preservation of Manning's rights."

Fort Meade is one of three bases within the Military District of Washington that have a courtroom that can accommodate the proceeding, according to a spokeswoman. Officials are making plans to address interest in the case from the national and international media.

The hearing is expected to last five days. But it is unclear how much of the proceeding will take place in public — and how deeply it will delve into classified matters.

"It's kind of a fan dance," said Fidell. "The government has to make the point that this was a disclosure, an awful disclosure, without revealing more than the bare minimum about our security measures — and about the corrective measures that have been undertaken, as I'm sure they have, after the release."

The leaked material

WikiLeaks published a broad range of classified U.S. documents beginning in 2010. They include:

• Video footage of a July 12, 2007, Apache helicopter attack in Baghdad that killed 12 people, including a Reuters journalist and his driver.

• Field reports from Afghanistan that included details of previously unreported civilian deaths and evidence of Pakistani and Iranian support of the Taliban.

• Field reports from Iraq that included details of previously unreported civilian deaths and reports of abuse, torture, rape and murder by Iraqi security forces.

• Diplomatic cables sent from embassies, consulates and other U.S. missions to the State Department between 1966 and 2010 containing analyses and assessments of foreign leaders and governments and economic and political conditions.

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