In World War II, the United States destroyed Nagasaki without pausing to see whether the first atom bomb, dropped on Hiroshima three days earlier, would induce Japanese surrender. Half a century later, few Americans complain about this incident. In World War II, the United States rounded up Japanese Americans and deprived them of their liberty. Half a century later, this wartime expedient is denounced as heinous. Incinerating a civilian is apparently better than locking him up, if the lockup is at home. Geography is everything.

Now consider the Bush administration's decision last week to authorize military tribunals for trying foreigners suspected of terrorist connections. The most troubling part was that these tribunals potentially may be set up at home, not just in Afghanistan or Pakistan. Abroad, tribunals seem possibly okay; after all, there's a war going on out there. At home, they are harder to stomach; after all, there's a Bill of Rights to protect here.

Is this geographic segregation tenable? You can certainly question it. It is easy for civil libertarians to denounce Japanese internment now, but the fact that the Supreme Court upheld the policy at the time shows that contemporary guardians of the Bill of Rights thought the issue was more complicated. World War II also offers a direct precedent for President Bush's military tribunals: Nazi agents caught on American soil were tried by military court, and the Supreme Court signed off on this.

If military tribunals on American soil were tolerable then, surely now the case is stronger? More than past wars, this one is being fought on the home front; there is a Homeland czar to prove it. Unlike past enemies, al Qaeda is not a territorial army with a few appended saboteurs; it is saboteurs, period.

Moreover, these saboteurs are scarier than any of their predecessors. In past wars against nations, the United States feared agents who might blow up dams, not aspirant martyrs who might nuke a city. Even terrorists used to understand limits. In 1944 two members of the Zionist Stern Gang were captured by an Egyptian policeman because they chose not to shoot him. Killing ordinary officials violated their terrorist principles.

If the nation is up against a ruthless foe who operates on its home turf, can't it use traditional courts to fight him? To a large extent it can and should; military tribunals are nobody's first option. But sometimes it may be impossible to prosecute without compromising an intelligence source, and that's a serious problem. In past wars, intelligence was one of many weapons. In the struggle against the foe in the shadows, intelligence is the weapon.

If America has used domestic tribunals in the past, and if a transnational, suicidal enemy makes them seem more necessary now, why should one resist them? The classic response is that ruthlessness is self-defeating. The successful terrorist movements of the past -- in Ireland prior to 1921, in Palestine in the 1940s, in Algeria in the 1950s -- have all won by inducing governments to carry out unpopular crackdowns that undermined their own legitimacy.

This is a good argument for restraint. But it is not an argument for restraint at home exceeding the restraint exercised externally. American legitimacy in this war depends on popular support abroad as well as at home; and in the CNN era, support at home is affected by the way we conduct the war externally. If anything, one might argue that restraint abroad is more important than restraint domestically, because the battle for public opinion abroad is a lot fiercer.

The truth is that the case for geographic segregation is not altogether logical. The United States fights a war to root out terrorist cells in Afghanistan, inevitably killing civilians along the way. It logically follows that it should fight terrorist cells at home, accepting some collateral damage to the civil liberties of foreign residents. But this is not the end of the debate: Powerful American ideals have a way of trumping logic.

Ever since the founding, Americans have believed they could build a City on the Hill, a fairly illogical ambition. They have believed they could avoid foreign entanglements, even when they could not; they have believed that if they made war, it was only to end future wars, even though this was impossible. American aspirations have set the country up for charges of hypocrisy and bouts of bitter disillusionment. Yet they have endured anyway, serving as an inspiration to the world. For this triumph over logic, we are all profoundly grateful.

President Bush, who once spoke of a "crusade" and of "Operation Infinite Justice," stands squarely within America's messianic traditions. When it comes to military tribunals, however, he has violated those same ideals and courted justified criticism. But it has to be said that this contradictory mixture belongs to the American tradition too. Abraham Lincoln, that greatest of American idealists, suspended habeas corpus.