IIRC he could have been released after 8 years. Let the courts do there job!
Its not just a court matter.
It's a matter of national policy.
If you want to continue allowing the illegal activities that gov agencies and officials are involved in, then you prosecute whistleblowers to the fullest extent. If you want to encourage more whistleblowers to uncover injustice, then you don't punish previous whistleblowers (who have provided great benefit to US citizens) to the fullest extent of the law. As I quoted articles earlier, many times it is impossible for a whistleblower to share important information about illegal activities without breaking the law or fear from retaliation.
It's Obamas right and job to follow the national policy that he kept promising to Americans. A court can't weigh the net benefits of the whistleblowing vs the crimes committed. They can only say, you committed XYZ and therefore deserve 35 years.