One administration official tells the reporters: "Civil liberties groups have encouraged the administration, that if a prolonged detention system were to be sought, to do it through executive order."
But it doesn't sound like those groups are pysched about the news, exactly. Shane Kadidal of the Center for Constitutional Rights told TPMmuckraker via email:
Prolonged imprisonment without trial is exactly the Guantanamo system that the President promised to shut down. Whatever form it takes - from Congress or the President's pen - it is anathema to the basic principles of American law and the courts will find it unconstitutional.
Another thing that's odd about this is the idea that this detention authority would somehow be more transient if it were authorized through executive order (which can be reversed at the stroke of the president's pen) rather than a statute (which could sit on the books indefinitely). If the last eight years have taught us anything, it's that executive abuses, left to continue unchecked for many years, have a tendency to congeal into precedent.