As I'm sure you're aware by now, the National Defense Authorization Act was passed by the House last night and the president is expected to sign it into law. Activists on the left are accusing Congress and the president of subverting civil liberties by signing the law due to the indefinite detention language in the bill. Mainly, the concern is that U.S. citizens could be indefinitely detained.
However, Rep. Adam Smith (D-WA), ranking member of the House Armed Services Committee, says the language explicitly prevents the indefinite detention of U.S. citizens.
First, the AUMF (Authorization for Use of Military Force) section in our bill, Section 1021, merely codifies current law. It specifically states, “nothing in this section shall be construed to affect existing law or authorities, relating to the detention of United States citizens, lawful resident aliens of the United States or any other persons who are captured or arrested in the United States.” Quite simply, our courts will decide what the law is regarding detention of U.S. citizens.
Second, any U.S. citizen detained under Section 1021 has the right under habeas corpus to have the legality of any such detention determined by our courts. The courts have also held that anyone detained under the AUMF at Guantanamo Bay, Cuba, also has habeas rights. We do not change these rights.
Third, Section , entitled, “Military Custody For Foreign al-Qaeda Terrorists” specifically excludes US citizens. It states, “the requirement to detain a person in military custody under this section does not extend to citizens of the United States.” It also states the requirement to detain under Section  “does not extend to a lawful resident alien of the United States on the basis of conduct taking place within the United States, except to the extent permitted by the Constitution of the United States.”
Fourth, we also codify periodic review for those being detained at Guantanamo Bay, now and in the future, which is an important procedure for those detained indefinitely as a threat to the United States under the law of war.
Habeas rights for any detainee irrespective of citizenship will remain intact (and backed up by the Supreme Court), and citizens can't be held in military custody. The reason the president decided to sign the bill and reversed his previous decision to veto the bill was because he wanted the discretion to hold civilian trials for suspected terrorists. The bill in its current form allows him to do that, hence the non-veto.
The bottom line here is the law merely codifies the current policy, which, admittedly, is ugly and questionable. If you really want to kill this thing, contact your senator. Tweeting impeachment threats at the president is tilting at windmills.