I have argued that the Executive branch should rely on military detention, not trial, for the GTMO population. In practice, this is what the Obama and Bush administrations have been doing, with tiny exceptions, for almost nine years. And Judges have upheld the practice for those enemy soldiers who fall within the AUMF.
But as time goes on, military detention may give rise to two problems.
The first is that the relevant war might end. This is hard to imagine right now with al Qaeda, but less hard to imagine with the Taliban, either because, as Bobby recently discussed, U.S. operations in Afghanistan might wind down, or because the Afghan government and the Taliban might reach a peace accord. When the relevant armed conflict ends, the justification for detention of soldiers in that war ends. If a particular soldier remains a threat to the United States at that point, he can probably only be held if convicted of a crime at trial. It is possible that the government could continue to detain a dangerous terrorist if it could convince a habeas court that he would re-start the relevant military conflict by re-attacking the United States if released. It is also possible that Congress could authorize preventive detention over still-dangerous terrorists after the relevant conflict ends. But these are long shots at best; trial or release is the likely option once the conflict ends.