Scott Horton, a contributing editor for Harper’s Magazine, said Wednesday that the National Defense Authorization Act was ambiguous about whether U.S. citizens who were suspected terrorists could be detained indefinitely.

"I think it makes clear that the law is locked in as it stands, but I think there is a lot of room for argument about how the law stood before this measure was enacted," he told Countdown host Keith Olbermann.

President Obama threatened to veto the entire defense bill because of the detainee provisions, which he said were “inconsistent with the fundamental American principle that our military does not patrol our streets.” But he later dropped his threat after the House-Senate conference committee amended the provisions by stating that the bill did not extend new authority to detain U.S. citizens.

U.S. Attorney General Eric Holder announced Wednesday that Obama would issue a signing statement when he signs the National Defense Authorization Act (NDAA) into law, but what the statement will affect is unknown.

"I think there are two major areas where the Obama administration pushed back," Horton said. "One area, fairly effectively, had to do with the president's authority in this area, his authority to direct prosecutions, choose the system that will be applied and so forth, and I think the Justice Department probably is going to say in signing this that he is not stepping back from the historical view of presidential powers in this area."

"But I think the area of greater concern is really with civil liberties, and I think there he is under considerable pressure to step up to the plate and say something about how he will apply this legislation consistent with the Constitution."

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