Manning was convicted Tuesday of 20 counts including theft and espionage, ten lesser charges of which he pleaded guilty to. Although he was acquitted of the most serious charge of aiding the enemy, he still faces 136 years in military prison.
As the judge, Army Col. Denise Lind, considers sentencing, the government is expected to call some 20 witnesses.
Elizabeth Dibble, principal deputy U.S. assistant secretary of State for Near Eastern affairs, testified Thursday about the effect Manning's leaks had on the State Department.
Dibble said that at the department's headquarters there was immediate "horror and disbelief that our diplomatic communications had been released and were available on public websites for the world to see."
She called U.S. embassies abroad our eyes and ears "on the ground" and said without trust and confidentiality a foreign official or country "will be burned."
When the defense asked Dibble about a statement from former Secretary of Defense Robert Gates that government secrets often "leak like a sieve," she said, "It makes a good sound bite, but I don’t agree with it."
Critics of the conviction say espionage laws have never been used against people who leak information to the press, rather, against actual spies and traitors, most recently during the Civil War.
Meanwhile, WikiLeaks founder Julian Assange called out President Obama for initiating "more espionage proceedings against whistle-blowers and publishers than all previous presidents combined."
"Manning’s alleged disclosures have exposed war crimes, sparked revolutions, and induced democratic reform. He is the quintessential whistle-blower," Assange wrote.