Justice Kennedy wrote the decision of the Court, authoring an opinion that traces the history of the "Great Writ" back to Magna Carta. Here's a snippet:
The Framers viewed freedom from unlawful restraint as a fundamental precept of liberty, and they understood the writ of habeas corpus as a vital instrument to secure that freedom. Experience taught, however, that the commonlaw writ all too often had been insufficient to guard against the abuse of monarchial power. That history counseled the necessity for specific language in the Constitution to secure the writ and ensure its place in our legal system.Let's just remember that this isn't the liberal, liberty-loving court of the 1950's and '60's. And as the Times reports, it's yet another "harsh rebuke of the Bush administration."
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The Framers’ inherent distrust of governmental power was the driving force behind the constitutional plan that allocated powers among three independent branches. This design serves not only to make Government accountable but also to secure individual liberty. Because the Constitution’s separation-of-powers structure, like the substantive guarantees of the Fifth and Fourteenth Amendments, protects persons as well as citizens, foreign nationals who have the privilege of litigating in our courts can seek to enforce separation-of-powers principles.
(internal citations omitted.)