alleged to have been fighting for al Qaeda or the Taliban? That was one of the issues in Hamdi and in Padilla.
A federal law, 18 U.S.C. 4001(a), says "No citizen shall be imprisoned or otherwise detained by the United States except pursuant to an Act of Congress." Padilla and Hamdi argued that as a result they couldn't be detained unless they were accused of having violated some federal criminal statute.
Not so, the government argued, the post-September 11 Authorization for Use of Military Force authorized 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." Such "necessray and appropriate force," the government reasoned, includes the power to detain enemy combatants, as well as the power to shoot them on the battlefield -- military force has always been understood to include the power of military detention.
Five of the Justices in Hamdi -- Justice O'Connor, joined by Chief Justice Rehnquist, Justice Kennedy, and Justice Breyer in the plurality, plus Justice Thomas in his dissenting opinion -- took the view that the Authorization allowed military detention at least of citizens who are "'part of or supporting forces hostile to the United States or coalition partners' in Afghanistan and who 'engaged in an armed conflict against the United States' there." That's why Hamdi lost on the statutory question.
But what about Padilla, who is alleged to be an enemy combatant, but who apparently wasn't engaged in an armed conflict against the United States in Afghanistan? Well, four of the Justices in Hamdi -- Justices Souter and Ginsburg, who partially concurred in Hamdi, and Justices Scalia and Stevens, who dissented -- disagree with the view I give above, and think that the Authorization doesn't apply even to Hamdi. It follows that they think it shouldn't apply to Padilla, either.
And in Padilla, which was disposed of on procedural grounds, Justice Stevens's dissent said, in footnote 8, that "I believe that the Non-Detention Act . . . prohibits -- and the Authorization for Use of Military Force Joint Resolution . . ., does not authorize -- the protracted, incommunicado detention of American citizens arrested in the United States." And the dissent was joined by Justices Souter, Ginsburg, and Breyer, who was in the plurality in Hamdi. So it sounds like five Justices think that Padilla should win on this statutory issue.
Now there is some question as to whether the five Justices' view of the 4001(a)/Authorization interplay in Hamdi is binding precedent. Lakewood v. Plain Dealer Publishing, 486 U.S. 750, 764 n.9 (1988), says that "when no single rationale commands a majority, 'the holding of the Court may be viewed as that position taken by those Members who concurred in the judgmen[t] on the narrowest grounds,'" and seems to reject the notion that one can add up votes from the plurality and the dissent. On the other hand, I suspect that lower courts will conclude that the five Justices' views are indeed binding on them.
On the other hand, I suspect that many lower courts would be reluctant to mix four Justices' views from one case (Hamdi) with one extra Justice's views in another (Padilla), especially when those views came in a footnote to a dissenting opinion written by another Justice (though, to be sure, an opinion that Justice Breyer did join without reservations). So in future cases involving Padilla -- I assume that Padilla can refile his case in the proper district, and thus avoid the procedural problem that led the Court to reject his claim -- lower courts would be free to conclude that Padilla loses on the 4001/Authorization question. What the Supreme Court will do with that, when and if Padilla's case comes back to the Justices, is impossible to tell, especially given that it could take years (assuming Padilla continues to be detained for that long), and some of the Justices might retire by then.