I agree with his statement that Congress has been the obstructionist here. In his words today:

Since taking office, I have repeatedly called upon the Congress to work with my Administration to close the detention facility at Guantanamo Bay, Cuba. The continued operation of the facility weakens our national security by draining resources, damaging our relationships with key allies and partners, and emboldening violent extremists.

For the past several years, the Congress has enacted unwarranted and burdensome restrictions that have impeded my ability to transfer detainees from Guantanamo.

On having the authority to try detainees in federal court:

The executive branch must have the authority to determine when and where to prosecute Guantanamo detainees, based on the facts and circumstances of each case and our national security interests. For decades, Republican and Democratic administrations have successfully prosecuted hundreds of terrorists in Federal court. Those prosecutions are a legitimate, effective, and powerful tool in our efforts to protect the Nation. Removing that tool from the executive branch does not serve our national security interests. Moreover, section 1034 would, under certain circumstances, violate constitutional separation of powers principles.

The statement ends with a bit of a veiled threat:

In the event that the restrictions on the transfer of Guantanamo detainees in sections 1034 and 1035 operate in a manner that violates constitutional separation of powers principles, my Administration will implement them in a manner that avoids the constitutional conflict.