Original link:
"Congress granted the president the authority to arrest and hold individuals accused of terrorism without due process under the NDAA,"
Your link:
"...enemy combatants, including U.S. citizens, but ruled that detainees who are U.S. citizens must have the rights of due process,"
We've got 2 issues there, 'enemy combatants' requires a bit more proof than 'suspected of terrorism', although things can be fudged like in the Bradley Manning case. Then we have the whole due process.
The 5th amendment:
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a grand jury, except in cases arising in the land or naval forces, or in the militia, when in actual service in time of war or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation."
The parts about the armed forces apply to military justice for troops, when wartime discipline is invoked. It's not saying that "when you're at war it all goes out the window for ordinary citizens".
Indefinitely detaining someone based on suspicion, without a requirement of due process or a way to appeal, is quite clearly unconstitutional although I hold little hope for the current Supreme Court to overturn it.