One of the ancient axioms of chemistry is, "The dose makes the poison." What may be beneficial in small doses can be harmful in large ones. A couple of aspirin can cure a headache, but a couple of hundred will kill the patient.

That insight applies in other areas, too. In wartime, you don't want the sort of president we had in, say, James Buchanan — who thought that while the South had no right to secede, he had no right to stop it, either. You want a president willing to act, quickly and forcefully.

But those qualities can be taken too far. If a powerful, assertive executive were an unmixed blessing, the United States would never have revolted against King George III.

From the beginning of the war on terror, the Bush administration has had two central objectives. The first is protecting the nation against its enemies. The second is asserting the president's near-absolute authority to wage this war. That approach involved a crucial error: It couldn't advance the second goal without undermining the first.

That's because ours is not a system designed to unleash the power of the government. It's a system designed to control it. By conceiving the president as a virtual monarch in national security matters, George W. Bush and his subordinates have provoked active resistance from both Congress and the courts — which might have been avoided with a more cooperative and pragmatic approach.

The latest illustration came Thursday, when the Supreme Court ruled by a 5-4 vote that the administration overstepped lawful bounds in its treatment of the detainees at Guantanamo. For the first time, the justices said foreign enemy combatants held outside our borders may appeal to the federal courts.

This is a welcome development because it upholds certain basic rights and safeguards that are due even to suspected terrorists. It's a worrisome development, on the other hand, because it requires the judiciary to assume grave responsibilities in a realm where it has no special competence.

The ideal is not for the courts to step into these matters. The ideal is for the elected branches to act with enough respect for constitutional values that the courts would see no need to step in.

But that happy optimum was not to be. The administration asserted that in time of war, even an unconventional war against a shadowy foe, the executive branch has the power to capture a foreigner abroad and hold him for the rest of his life, without any independent review by the courts.

Short of claiming the right to do that to an American citizen arrested on U.S. soil — a claim the administration had also made, only to see it repudiated by the courts — that's about as vast and dangerous a power as you could find. So it is not surprising that the Supreme Court balked.

The justices insisted that the constitutional guarantee of habeas corpus, which lets prisoners challenge their confinement, must be respected. Except when Congress formally suspends that right, wrote Justice Anthony Kennedy, it assures that "the judiciary will have a time-tested device … to maintain the 'delicate balance of governance' that is itself the surest safeguard of liberty."

The response among the administration's allies on Capitol Hill was predictably angry. Republican Sen. Kit Bond of Missouri said the court "chose to give foreign terrorists the constitutional rights and privileges of U.S. citizens."

But the constitution is very clear in extending protections to non-citizens present on sovereign U.S. territory or the functional equivalent, which Guantanamo clearly is. And how does Bond know the inmates are terrorists? The court's chief objection was that the existing review process gives detainees no plausible means to demonstrate their innocence.

Such measures may be unnecessary if you're fighting the Wehrmacht or the Imperial Japanese Navy, whose members are easy to identify. But against an adversary like al-Qaida, mistakes are far more likely — and, given the open-ended nature of the conflict, far more harmful.

So if Congress and the president refuse to provide the checks needed to guard against error and abuse, they should not be surprised to find them imposed by the courts. Whatever the Supreme Court may not know about fighting a war, it knows something the elected branches should have kept in mind: In America, the only legitimate power is a limited power.

Steve Chapman blogs daily at newsblogs.chicagotribune.com/steve_chapman. To find out more about Steve Chapman, and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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