THE FIVE-YEAR LEGAL DEBATE over the global war on terror has focused predominantly on first principles: What does our Constitution allow? What does it forbid? But in those five years, three of the Supreme Court’s four decisions have rested on statutory, not constitutional, grounds. The recent debate over the Military Commissions Act suggests that many legislators and commentators can’t tell the difference between the two.

Of the MCA’s various controversial provisions, the most mischaracterized was its amendment of 28 U.S.C. 2241, limiting the right of detainees to petition the federal courts for the “writ of habeas corpus”–i.e., to challenge the legality of their detention. The Los Angeles Times, for instance, warned that, “[b]y preventing detainees from challenging their confinement in court, it sets up a potential constitutional conflict before the Supreme Court.” Senator Patrick Leahy flatly announced that, “[t]his is wrong; it is unconstitutional; it is un-American.”