What would happen if another 19 well-trained Al Qaeda terrorists, this time with 19 bombs in their bags, tried to board 19 airliners over the next 19 months? Many would probably succeed, blowing up lots of planes and thousands of people, if the forces of head-in-the-sand political correctness prevail-as they did before September 11-in blocking use of national origin as a factor in deciding which passengers’ bags to search with extra care.

But a well-designed profiling system might well catch all 19. Such a system would not be race-based; indeed, most Arab-Americans would not fit the profile. It would factor in suspicious behavior, along with national origin, gender, and age. It could spread the burden by selecting at least one white (or black, or Asian) passenger to be searched for every Middle Easterner so selected. And it should be done politely and respectfully.

We have no good alternative. For the foreseeable future, the shortage of high-tech bomb-detection machines and the long delays required to search luggage by hand will make it impossible to effectively screen more than a small percentage of checked bags. The only real protection is to make national origin a key factor in choosing those bags. Otherwise, federalizing airport security and confiscating toenail clippers will be futile gestures.

I revisit this issue in part because research since my September 22 column reinforces my conviction that national-origin profiling may be the only way (in the short term) to avoid hundreds or thousands of deaths. At the same time, critics have persuaded me that the "racial" profiling of "Arab-looking" people that I previously advocated would be less effective than profiling based on apparent origin in any of the nations known to be exporters of anti-American terrorism-not only nations in the Arab world, but also most, or all, of the nations in the Muslim world. Millions of Arab-Americans would not fit the profile because their American roots would be apparent-from their accents and speech patterns-to trained security screeners.

We have heard a great deal about the hurt feelings of Middle Eastern passengers who have been searched and (in some cases) rudely treated on flights or unjustifiably ejected from airliners. We have heard far less about the dangers of not searching. The reason is that "large and important parts of the American news media practice a virulent form of political correctness that is indistinguishable from censorship," in the words of Richard Cohen, the mostly liberal Washington Post columnist.

Opponents of national-origin profiling claim it would be more effective to focus solely on suspicious behavior. They are wrong. Competent terrorists know how to avoid the suspicious-behavior trap. They are not likely to buy one-way tickets the next time. Or to pay in cash. Or to fly from Afghanistan to Pakistan to New York. Or to hang around airport security checkpoints with video cameras. These people are not stupid.