An amendment sponsored by Sen. Dianne Feinstein (D-Calif.) says the relevant section of the NDAA doesn't change "existing law" with regards to the detention of US citizens, permanent legal residents, and terrorist suspects captured in the United States. The problem is that there's a debate over what "existing law" is.
Civil liberties advocates and some members of Congress argue that the government can only indefinitely detain an American if he is, as Feinstein explained on the Senate floor , "taken an active part in hostilities against the United States and is captured outside the United States in an area of 'active combat operations,' such as the battlefields of Afghanistan."
But many legal experts, members of Congress, and both the Bush and Obama administrations have argued that existing law allows the US to indefinitely detain all people, including American citizens, who the president determines are part of or "substantially supported" Al Qaeda, the Taliban, or associated forces. (You can see an Obama administration argument on this subject here .) The Supreme Court has yet to issue a definitive ruling on the issue.
As I reported in the September/October issue of Mother Jones , the US government has a longstanding program it uses to facilitate the detention and interrogation of US-born terrorist suspects captured abroad. Through the program, which critics refer to as "proxy detention," the US government encourages foreign regimes to detain and interrogate Americans it suspects of involvement in terrorist activity. The country holding the American terror suspect often receives questions from and transmits answers back to US authorities. Although the program raises civil liberties concerns, especially in cases where American detainees claim to have been abused in foreign custody, it's not necessarily illegal-and now, with the passage of the NDAA,, the transfer of terrorist suspects to foreign countries has formal congressional sanction.