The debate in Congress focused almost exclusively on physical security: airport inspections and undercover sky marshals. Because there are not enough marshals for every flight, the airport must become a final, formidable line of defense. Though the new law appears to strengthen airport security, it fails to make use of government and commercial databases that would allow a federal agency to identify everyone who makes a reservation.

This is not about ethnic profiling. Compiling a massive dossier on each passenger would waste time as well as resources. The objective of preflight screening is to pinpoint those passengers about whom we know little or nothing.

With screening information attached to each reservation, airport security officials could concentrate their resources on the relatively few passengers who cannot be adequately verified through public and private-sector databases. Individuals for whom little information exists should face greater scrutiny than those who are well established in their communities.

A picture I.D., such as a driver’s license, is not enough. Most state motor vehicle departments require only two forms of identification from a new applicant. As a practical matter it takes only one “breeder document,” such as a passport, to generate additional documents. With a false passport, a foreign resident in the United States can get a student or employee I.D., establish a bank account and obtain other documents based on the passport. With these documents, foreigners can handily obtain a state driver’s license.

When passengers check in for a flight, airlines look only at the outward trappings of identity, such as a driver’s license or passport. A true security system would search for corroborating data to determine the depth of information associated with those documents.

When someone presents a credit card to cover a purchase, an online system verifies the validity of the card and approves the charge if the amount does not exceed the cardholder’s authorization level. Financial institutions routinely review credit and banking records when someone applies for a home or car loan. A federal agency charged with aviation security ought to have similar access to determine if the name, address and credit card number linked to a flight reservation are legitimately connected to the individual who made the reservation.

The end result of such preflight screening would be a score that weighs the quality and quantity of data related to each passenger. An individual with long-standing ties in this country — employment, residence, tax payments — will score high. Someone who has left few traces in government and commercial databases will score low.

Take the 19 hijackers. All had applied for, and received, Social Security numbers; yet an examination of Social Security records would have shown few with significant earnings. Similarly, some of the terrorists had frequent flier numbers but few or no mileage credits.

Had a competent federal agency been operating a preflight screening system, we could have penetrated the cover of the 19 terrorists. Their employment and income records would have been thin to nonexistent. The agency would have found some using box numbers at Mail Boxes Etc. instead of street addresses. An automated match against watch lists could conceivably have triggered an investigation and possible arrests. At a minimum, their low screening scores would have been appended to their flight reservation records and alerted airline and airport security staff to thoroughly inspect the men and their baggage.

At airports today, passenger check-in and security checkpoints operate independently or, more to the point, in ignorance of each other. The new law does not address this.

If we had an integrated system, the agency could physically track individuals from the moment they come into contact with the airline or a security checkpoint. The number on each passenger’s ticket would link the flight reservation to the preflight screening score. Though the score would be invisible to the passenger, everyone connected to air travel security would have access to the information.

The checked luggage of someone with a low score would be X-rayed and opened, if necessary, to make certain it posed no danger to the flight. At security checkpoints, passengers would be directed to specific lines. Those with low scores would go to lines that specialize in detailed electronic and physical inspections of individuals and their carry-on baggage.

Having a federal agency track everyone through the security process would also make airport screening more efficient. Instead of the mob scene now playing at major airports, with everyone vying for the same lines, the tracking process could automatically assign passengers whose boarding times are fast approaching to shorter inspection lines.

All passengers and their luggage must be inspected, if only to prevent someone from hiding a bomb in the suitcase of an innocent passenger. But an intelligent security system cannot treat everyone the same way; it must focus on those most likely to pose a risk.

The terrorists had their flight reservations two weeks before Sept. 11. The airlines’ antiquated hijacker profile — one-way ticket, purchased in cash at the last minute — proved useless. Some of the terrorists used online reservation systems and paid with credit cards. Inspectors at each airport missed the box cutters concealed in their carry-on bags. The terrorists all too easily worked their way through our fragmentary system.

The new law perpetuates that fragmentation.

A virtual conspiracy has the same objective — to depose a leader — but the means are different. A virtual conspiracy starts in the open and requires publicity to flourish and gain adherents. Virtual conspirators test-fly stratagems, tactics and rumors. They do not meet in secret until they have discerned what will advance their undertaking and what will not. Moreover, by making their initial moves in the open, they attract others to their cause and to one another.

Instantaneous communication is critical to a virtual conspiracy. So, too, is freedom of expression. Though there are laws against making false accusations, virtual conspirators who channel charges, allegations and rumors through the press or spread them on the Internet gain the protection of the First Amendment. Most thrusts fail, but some wound, making the hated target more vulnerable the next time around.

Sound far-fetched? Consider:

• Did the president or first lady have a hand in the death of Vincent Foster? A virtual conspirator couldn’t care less if there’s any basis to ask the question. The objective is to get the media to float the idea of the Clintons as murderers, see if it resonates with the public and then hope that someone will come forth with proof. The evidence indicates Foster committed suicide.

• Did the president lurk in the back of a limousine and sneak out of the White House for sexual trysts at the local Marriott? There was no reason to believe he did, but that didn’t stop an author from scripting the scenario — and his publisher from promoting it — to push the book toward bestseller status.

• Did the Clinton administration allocate grave sites at Arlington National Cemetery for political supporters? The far right jumped with righteous glee on that one because it sounded too good not to be true. And who knows? A sergeant in Graves Registration might have stepped forward with a treasure trove of documents and transmuted the brass of speculation into the gold of truth. No one did.

• Did Clinton rape a woman in Arkansas when he was attorney general in his home state? His opponents recently leaked that tale, which the press printed, even though the alleged victim denied such an attack ever took place.

Four provocative questions, each answered in the negative, yet each somehow wormed its way into “the news.” How did these fabrications gain such wide dissemination? Who peddled them to the press? Of course, the reporters in the best position to answer have sources to protect.

Here, then, is the wonderful thing about being a virtual conspirator: You can spread rumors, speculation and lies against your enemy and not be called to account. The reporter you conned into retailing a falsehood may cuss you out, but that reporter is not going to expose you. The president you’ve maligned won’t sue because he’s already so heavily in debt to his lawyers. Moreover, as a public figure, he would need to demonstrate actual malice to win a judgment — assuming his attorneys could determine who to sue in the first place. Besides, an angry denial generates yet more coverage of the charge itself.

Because it encourages freelance attacks on the flimsiest of pretexts, a virtual conspiracy can misfire and produce some measure of sympathy for the president — and polls suggest it is doing just that. However, the piling on of unsavory allegations inevitably exacts a toll, adding to public skepticism about Clinton and laying the groundwork for some future revelation that could suddenly puncture his cushion of popularity.

How do virtual conspirators go after a president they can’t defeat at the polls? They turn, naturally, to the two great corrupters of humankind: money and sex.

For urban or suburban politicians, the typical lure is unmarked cash or overseas bank accounts from building contractors who need help with zoning permits or bids to pave highways. Their rural counterparts get caught up in land deals, playing silent partner and leveraging a minuscule investment into a windfall when the shopping center, subdivision or resort goes up.

The temptations of the flesh require no elaboration. You can read about them in the Bible or browse them on the Internet. King David was neither the first national leader nor the last to make a move on the wrong woman.

What of Clinton, erstwhile governor of Arkansas and current president of the United States? Whether you love him or hate him, there’s no gainsaying the man’s political prowess. Among contemporary politicians, there’s Clinton — and there’s everybody else. Since his entrance onto the national stage, the virtual conspiracy has launched at least four major efforts to undo him, using tactics that have succeeded against other politicians.

Gambit No. 1: Extramarital sex

In times past, a prominent politician who had a sexual affair was finished. The swift rise of Gary Hart to front-runner status for the Democratic nomination in 1988 and even swifter decline after an extramarital affair was revealed was the most recent case in point when Clinton began his run for the White House.

Enter Gennifer Flowers on the eve of the 1992 New Hampshire primary, with claims of a long-standing affair and audiotapes of someone who sounded mighty like the man from Hope. Instead of folding under pressure, Bill and Hillary Clinton faced the cameras together. One year later, they were picking fabric for the family quarters in the White House.

Gambit No. 2: Corrupt land deal

When extramarital sex didn’t sell, the virtual conspirators turned to money. It says something about their desperation that they focused not on a windfall that enriched Clinton but on a money-loser called Whitewater. Four years and $40 million later, an independent counsel has yet to come up with something damning against Clinton — and not for lack of trying.

Gambit No. 3: Sexual harassment

The provenance of the Paula Jones case, recently thrown out of federal district court in Little Rock, fits perfectly with the concept of a virtual conspiracy. Clinton had gone to Washington and Paula Jones had gotten on with her life when a writer for a right-wing magazine digging into Clinton’s past came up with allegations of a spurned advance against someone identified only as Paula.

At the time the article came out, stories of Clinton’s amatory adventures down home were as plentiful as tabloid sightings of Elvis. The hard core of Clinton haters in Arkansas regularly regaled visiting scribes with such tales, some of which squirmed their way into print. In short, the contention that someone named Paula, Polly, Patsy or Peggy might have had a fling with Bill was not exactly a thunderbolt. Thereupon, Paula Jones stepped forward and identified herself as that Paula, avowedly to clear her heretofore unsullied, unknown last name. She did so with the very public assistance of a miniphalanx of right-wing lawyers and, later, the support of a well-funded foundation. The virtual conspiracy was now starting to look more and more like the real thing.

Trotted out in advance of the 1996 election, the Jones gambit tottered but did not quite fall. When the Supreme Court ruled that a sitting president could be compelled to testify in a civil suit, the conspirators suddenly found the ideal vehicle for their next venture.

Gambit No. 4: Turning sex into perjury

News accounts indicate that attorneys for Jones took a deposition from the president in which they interrogated him about alleged extramarital affairs. Would a recent affair between consenting adults be relevant to determining what might have happened in a Little Rock hotel room seven years before? Obviously not. But the court’s ruling made it open season on Clinton.

It proved a perfect trap. Think about it: What choice does a husband have when questioned about cheating? If he admits an affair, he risks his wife’s divorcing him. If he denies it, he gains another chance to change his ways and save his marriage. Admirable, no — but altogether human and understandable.

Most such confrontations occur in private between husbands and wives and are resolved by them, one way or another. Some may get divorced, but none will have family, friends and associates hauled before a grand jury by a prosecutor bent on nailing the individual on charges of perjury or worse. Yet, that is precisely the situation that now mesmerizes the independent counsel, the press, a grand jury and countless millions of us mere voyeurs.

The interrogators had listened to hours of tape-recorded conversations between an anxious young woman and an older confidante motivated by something other than friendship when she clicked the on switch. The lawyers set the strategy, rehearsed their tactics, then launched their attack.

The virtual conspiracy demonstrated it had learned from its mistakes in Gambits No. 1, 2 and 3. The tapes alone would have been useless — an obvious lesson from Gambit No. 1. But those tapes in the hands of Jones’ lawyers and the independent counsel allowed the conspirators to execute Gambit No. 4 in concert and move closer to their ultimate goal: undoing our two most recent presidential elections.

The motivation of the virtual conspirators is transparent: By their deeds, we have come to know them. For some time now, they have been delving into matters financial and sexual, probing for points of vulnerability. In communicating those intentions so openly, they attracted comrades with something to offer: money, attorneys, tape recordings.

Only one mystery remains: Knowing exactly where he might be vulnerable, why did a politician as smart and wily as Clinton allow himself to be outmaneuvered?