The explosion at the United Nations headquarters in Baghdad, combined with the daily reports of Americans shot, blown up and otherwise ambushed, is making some Americans queasy about the job of reconstruction in Iraq. We know what the head-in-the-sand crowd is going to say. "Bring Them On?" asks the Nation magazine, no, "Bring Them Home."

But bringing them home would be the worst possible response to the violence -- though not one unprecedented in recent American history. When our troops in Beirut were blown up by terrorists, Ronald Reagan brought them home -- not instantly, but eventually. When the terrorists in Somalia dragged the bodies of our men through the streets of Mogadishu, President Clinton brought them home and thus sent a signal to Osama bin Laden and others.

Here is what the chief terrorist told ABC's John Miller in 1998: "We have seen in the last decade the decline of the American government and the weaknesses of the American soldier, who is ready to wage cold wars and unprepared to fight long wars. This was proven in Beirut when the Marines fled after two explosions. It also proves they can run in less than 24 hours, and this was also repeated in Somalia. ... Our youth were surprised at the low morale of the American soldiers. ... After a few blows, they ran in defeat. ... They forgot about being the world leader and leader of the new world order. (They) left, dragging their corpses and their shameful defeat."

As Reagan was known to say in a different context, "Weakness is provocative."

Bin Laden's wings have been severely clipped since 9-11, and he is no longer free to meet reporters in the open. But while he lives he remains a threat, as do too many of his co-religionists (meaning Islamists, not all Muslims).

So whether it is easy or hard, we must stay in Iraq and transform it into something reasonably approaching a free and open society. If we demonstrate any lack of resolve now that we have achieved real momentum in the war on terror, all of the victories we've achieved will turn to dust.

Unlike our efforts in Lebanon and Somalia, our engagement in Iraq is not primarily motivated by humanitarian impulses (though it has obvious humanitarian dividends). We are engaged in Iraq because it was one of the chief terror sponsors in the world. President Gloria Arroyo of the Philippines has said that "the Iraqi regime was supporting terrorist cells all over the world. We had to expel three Iraqi diplomats from the Philippines because of evidence that they were either in touch with Abu Sayyaf or doing their own espionage."

As the daily headlines make clear, the task is not going to be easy. Historian Douglas Porch, writing in The National Interest, argues that the occupation of Japan and Germany didn't go swimmingly, either. "American occupiers assumed that, once the virus of authoritarian rule had been purged, grateful Japanese and Germans would enthusiastically embrace democracy. Instead, U.S. reformers encountered torpor, resentment and resistance."

The de-Nazification process, now recalled as a stunning success, was perceived at the time as a failure because it created a "community of fate" between the lowest Nazi functionary and the Gestapo. And Konrad Adenauer complained that if he followed U.S. guidelines, only Germans over 65 and those under 20 would have qualified for government service.

Porch believes that the existence of a common enemy, the Soviet Union, drove the Japanese and Germans gratefully under the American wing. But as he himself acknowledges, it was more than that. In Japan, officeholders agreed to adopt MacArthur's program, including "land and labor reform, decentralization of the police, female suffrage, education and judicial reform, and a new constitution," while secretly planning to repeal them. But the Japanese people became quite attached to their new freedoms and declined to relinquish them.

There is no democratic tradition in Iraq or anywhere else in the Arab world on which to draw. Theirs is a society permeated by lies and deception, and a religion that is dancing with extremism. These are not good candidates for democracy, and Iraq is never going to be Indiana. But if, in 20 years, it looks more like Turkey than like Syria, Iraqis and the rest of the world, not least the United States, will be far, far safer.