Hamdi v. Rumsfeld

Majority reasoning

The plurality reasoned that detaining combatants captured on a foreign battlefield is a fundamental and traditional incident of waging war, so Congress's authorization of "necessary and appropriate force" implicitly included authority to detain such individuals, satisfying the statutory requirement that no citizen be detained except pursuant to an Act of Congress. It rejected the government's position that courts should defer entirely to the executive's say-so, holding instead that due process under the Fifth Amendment requires weighing the citizen's fundamental liberty interest against the government's security interests using the balancing test from Mathews v. Eldridge. The plurality concluded that citizens must get notice of the factual basis for their detention and a fair opportunity to rebut it before a neutral decisionmaker, though hearsay evidence and a rebuttable presumption favoring the government's evidence could be permitted to reduce burdens on the military. The plurality also directly responded to Justice Scalia's reliance on Ex parte Milligan and the New York War of 1812 cases, arguing that Ex parte Quirin already rejected that reading of Milligan and that battlefield capture, not mere concession of enemy status, is what matters.

Dissent reasoning

Justice Scalia, joined by Justice Stevens, argued that the historical and constitutional tradition offers only two lawful paths for holding a citizen accused of fighting against the country: criminal prosecution for treason or another crime, or a formal congressional suspension of the writ of habeas corpus under the Suspension Clause. He traced English and American legal history, including the Habeas Corpus Act of 1679, the Founders' writings, and Civil War-era cases, to show that indefinite detention without charge or suspension has never been an accepted middle path for citizens. He argued the AUMF is not a suspension of habeas corpus and does not clearly authorize detention with the specificity required to overcome the Non-Detention Act, and criticized the plurality for inventing an ad hoc due-process procedure that neither Congress nor the Constitution provides. Justice Thomas, dissenting separately, argued that the decision whether Hamdi is an enemy combatant is a quintessential war-making and national-security judgment committed to the executive, which courts lack the expertise and constitutional authority to second-guess. He contended that under precedents like Moyer v. Peabody, due process requires only a good-faith executive determination in this context, and that even under the plurality's own Mathews balancing test, the government's compelling national security interest should have prevailed, since additional judicial process risks compromising intelligence-gathering and disclosing classified information.