So? Charge him and deny bail. A simple prima facie case could keep him in detention. If there is evidence enought to prove him an enemy combatant, there evidence enough to strip him of his citizenship and hold him militarilly for a military tribunal. Nothing you have said is supported by anything other than the word of the Justice Dept.
Do you trust your elected officials and appointed bureaucrats so much that you will put your own liberty in their hand on their word only? This is why the Founders established due process. They know how untrustworthy a government run by human beings is.
By your willingness to accept such shenanigans without question, you place my, as well as your, liberty and well being at risk. All government forms in history, especially elderly ones like ours, has been studies in corruption and power seeking. What in the hell makes you think this one is any different?