month over his massive leak of US military intelligence reports and diplomatic cables.
The defence opened its case on Monday in the sentencing phase of the trial by focusing on alleged shortcomings in the chain of command, questioning officers about how they handled concerns over Manning's mental condition and whether he should have retained his security clearance.
Several officers, including the commander of Manning's brigade from the 10th Mountain Division, Colonel David Miller, said the unit faced a shortage of intelligence analysts but denied sending Manning or other soldiers to Iraq who were not fit for duty.
"In a counterinsurgency fight, you can always use more," intelligence analysts, Miller told the court.
Miller said he was unaware at the time of an incident in Iraq when Manning had flipped over a table and had to be restrained during a counseling session.
The junior intelligence analyst had "a problem getting along with people", according to the head of the brigade's intelligence section, Major Cliff Clausen, citing an account from his deputy.
The company commander, Captain Matthew Freeburg, told the court he was surprised that the military had not taken more severe disciplinary action against Manning before he was accused of assaulting another soldier.
Freeburg said he "found it strange" that "something more hadn't been done."
The captain demoted Manning over the incident and removed him from the intelligence office, filing paper work that he expected would strip the soldier of his security clearance and possibly expel him from the force.
The defence honed in on an internal military investigation after Manning's leak, which quoted officers describing the head of the soldier's intelligence office and a deputy as "weak" leaders.
Both the brigade commander and his executive officer, Lieutenant Colonel Brian Kerns, testified that the head of the brigade's intelligence section, Clausen, was removed from his position in early 2010 because he had difficulty conveying intelligence findings to commanders.
Before the brigade left for Iraq, top officers had concerns about the shortcomings of the intelligence chief and a sergeant under him, according to Kerns.
"We understood some of the ramifactions of not having the ideal team in there," Kerns said.
Manning's sentencing hearing is scheduled to last until August 23 and his defence attorney, David Coombs, has said his client will make a statement to the court during the proceedings.
Manning was working as an intelligence analyst near Baghdad when he was arrested more than three years ago over the document dump to WikiLeaks.
Before his trial began, Manning admitted to handing over 700,000 classified documents to the anti-secrecy website founded by Julian Assange.
Manning was cleared of the most serious charge against him, that he had leaked the documents to knowingly help America's enemies, but he could still spend the rest of his life in prison.
Manning, the son of an American father and Welsh mother who later divorced, said he passed the documents to WikiLeaks to ignite a public debate and reveal the true face of America's wars.