bingo, this protects the President for things that have already happened.
This NDAA is putting a Congressional stamp of approval on the long detentions which Bush and Obama have already commited, especially for foreign nationals snatched up abroad, such as in Afghanistan, or Africa, Arabia, Europe, etc. and also in the USA.
This should help protect Presidents Bush and Obama from being arrested on charges of war crimes or kidnapping when they travel outside the US. They can claim that their actions were legal under US law.
Many people have asked 'What is behind this?', 'Why is this coming up right now?', 'Who is pushing for this?', etc.
And here is a possible explanation.