In 2013, Manning was sentenced to 35 years of imprisonment for releasing confidential military and State Department documents.
The sentence was then commuted by the then-President Obama toseven years, dating from the beginning of her confinement in 2010.
"My conscience and duty to the men and women of the Central Intelligence Agency will not permit me to betray their trust by appearingto support Harvard'sdecisionwith my appearanceat tonight's event," Pompeo said in a letter to the Ivy League university.
"Wikileaks is an enemy of the US, akin to a hostile foreign intelligence service. Leaders from both politicalparties denouncedMs Manning's actions as traitorous and many intelligence and military officials believe those leaks put the lives of the patriotic men and women at the CIA in danger. And those military and intelligence officialsare right," he said.
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"Indeed, Ms Manning stands against everything the brave men and women I serve alongside stand for. Let me be clear, this has nothing to do with Ms. Manning's identity as a transgender person. It has everything to do with her identity as a traitor to the United States of America and my loyalty to the officers of the CIA," Pompeo said in his letter.
"While I have served my country as a soldier in the United States Army and will continue to defend Ms Manning's right to offer a defense ofwhy she chose this path, I believe it is shameful for Harvard to place its stamp of approval upon her treasonous actions," he said.
Former CIA Deputy Director Michael Morell also resigned from his post as a senior fellow at Harvard Kennedy School after the university announced to have hired Chelsea Manning as a visiting fellow.