As the swing vote on a polarized United States Supreme Court, Justice Anthony Kennedy is among the most powerful men in the country.

With yesterday’s 5-4 decision in Boumediene v. Bush, Kennedy, who authored the majority opinion, showed that not only is he very comfortable with power, he is also intent on shoring up and expanding the power of the federal judiciary system that he sits atop.

The case dealt with alien enemy combatants held at Guantanamo Bay Naval Base, located on a patch of Cuban soil leased by the US since 1898. The quirky nature of the territory raises questions about the reach of the Constitution there.

In Boumediene, the Kennedy-led majority concluded that prisoners held at Guantanamo have the right under the Constitution to petition for a writ of habeas corpus — that is, to petition for a release — under the Suspension Clause (“The privilege of the writ of habeas corpus shall not be suspended, unless when in cases of rebellion or invasion the public safety may require it”).

Justice Antonin Scalia argues fairly persuasively in his dissent that it this is an incorrect reading of the precedent and history surrounding habeas corpus. But the Kennedy-led majority does more than merely give detainees a mechanism for challenging their detention.

The Military Commissions Act and the Detainee Treatment Act already provide such a mechanism, which Chief Justice John Roberts elaborates on in his dissent. (Scalia and Roberts joined each other’s dissents, and Clarence Thomas and Samuel Alito joined both dissents.) What the majority has done is give detainees the right to file a habeas petition in civilian federal court.

This is bound to cause a lot of problems that the MCA and DTA were designed to avoid. The whole purpose of these laws was to avoid habeas petitions in open court. They established the Combatant Status Review Tribunal (CSRT) for detainees to appeal to, and gave the DC Circuit Court jurisdiction over appeals from the CSRT. This system has yet to be tested, as detainee lawyers have preferred to file federal lawsuits to circumvent the tribunal system, a tactic that has now succeeded.

The Military Commissions Act was passed in the wake of Hamdan v. Rumsfeld, in which, as Scalia points out, four of the five justices in the Boumediene majority joined an opinion in stating that “Nothing prevents the President from returning to Congress to seek the authority [for trial by military commission] he believes necessary.”

Adds Scalia, after quoting this: “Turns out they were just kidding.”

INDEED, KENNEDY and the majority seem dead-set against reading the statutory law in a way that will satisfy them. “To hold that the detainees at Guantanamo may, under the DTA, challenge the President’s legal authority to detain them, contest the CSRT’s findings of fact, supplement the record on review with newly discovered or previously unavailable evidence, and request an order of release would come close to reinstating the §2241 habeas corpus process [that is, the standard process for noncombatant American citizens] Congress sought to deny them,” writes Kennedy.

“In other words,” responds Roberts, “any interpretation of the statute that would make it an adequate substitute for habeas must be rejected, because Congress could not possibly have intended to enact an adequate substitute for habeas.”

Of course, an adequate substitute for habeas is exactly what Congress intended to enact. The goal was to find a Constitutionally acceptable framework for trying combatants without the constraints and dangers of civilian court.

One classic example of what can go wrong, it came out in open court during the 1995 prosecution of Omar Abdel Rahman for the first World Trade Center bombing that US authorities were monitoring terrorists’ cell phones. Terrorists promptly stopped using them.

Kennedy et al. punt on what to do about issues like that, leaving it to the lower courts to figure out. “The majority merely replaces a review system designed by the people’s representatives with a set of shapeless procedures to be defined by federal courts at some future date,” writes Roberts. “One cannot help but think…that this decision is not really about the detainees at all, but about control of federal policy regarding enemy combatants.”

Scalia is blunter: “What drives today’s decision is neither the meaning of the Suspension Clause, nor the principles of our precedents, but rather an inflated notion of judicial supremacy.”

In an already much-quoted passage, Scalia writes that this decision “will almost certainly cause more Americans to be killed.” He closes his dissent with the assertion that “The Nation will live to regret what the Court has done today.”

He’s probably right. But Anthony Kennedy is Lord of the Judiciary, and nothing can stop him when he’s intent on expanding his fiefdom.