Volokh has comments on Padilla vs. Rumsfeld. He agrees with the dissent. The ruling was that a citizen can’t be detained except by an act of Congress. The Joint Resolution authorizes the President
“to use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons.”
The government argued that this is the act of Congress which authorizes it, but the majority opinion was that this did not explicitly authorize detention of citizens clearly enough. Seems like a silly opinion to me. I hope Volokh’s right, and it gets reversed in the Supreme Court.