A few comments from Professor Johannes:
"Technically, a law was broken; the president is required to consult 30 days before releasing prisoners. Much like the War Powers Act, which every president has claimed to unconstitutionally restrict their commander-in-chief and chief executive authority, Obama and his team deny the applicability of the Guantanamo law to this release. They've also claimed urgency and said that there had been past consultations such that they'd met the requirements, given the urgency of this particular prisoner swap deal.
This is similar to Obama's denial that the War Powers Act applied to his use of U.S. planes over Libya a couple years ago.
Three realities. First, the courts will not get involved, leaving this to interplay between Congress (at least its Republicans) and the White House, State Department, and other agencies.
Second, this fits a pattern that goes back to 1974 when the War Powers Act was enacted. Congress demands consultation and subsequent reporting; presidents sometimes do and sometimes don't consult -- sometimes they don't even notify -- but they typically do report but NOT "in pursuance" of the War Powers Act but rather "cognizant of" or "consistent with" it.
Third, this will again inflame partisan warfare. We can expect, as in Benghazi, congressional hearings, proposals to impeach, and lots of media heat. Recriminations all over the place.
In the end, nothing will happen. The deal is done. Presidents always win these battles, but in the process they do suffer some cuts and bruises."