Navy Cmdr. Youssef Aboul-Enein is set to testify today at Manning's sentencing hearing at Fort Meade, near Baltimore.
The witness is the author of the book, "Militant Islamic Idealogy." He's also a top adviser at the Pentagon's Joint Intelligence Task Force for Combating Terrorism. He argued that winning the war against militant Islamists requires a nuanced understanding of their ideology.
Manning faces up to 90 years in prison for giving more than 700,000 documents, along with some battlefield video, to the anti-secrecy group while working as an intelligence analyst in Iraq in 2010.
The judge ruled that such testimony is admissible only if the effect came directly after the information was published. She also rejected Acting Assistant Secretary Michael Kozak's testimony that the leaks had made some foreign citizens, including human rights activists, less willing to speak privately with US diplomats.
The judge heard the testimony from a military intelligence official and civilian James McCarl who leads a Pentagon effort to analyze information about the enemy's use of homemade bombs or improvised explosive devices which McCarl said accounted for 60 to 80 per cent of all casualties in Iraq and Afghanistan.