Make no mistake about it, after last Tuesday traveling in America will never be the same.
For the past decade, as concern about terrorism increased, then ebbed, along with its presence in the headlines, security at the nation's airports has increased in some measure.
But it has never reached the levels recommended by security experts and commissions set up in the wake of the 1988 bombing of PanAm Flight 103 and the loss of TWA Flight 800 in 1996.
Indeed, even with all of the screenings, baggage searches, identification checks, and metal detectors, some experts contend security at the nation's airports is often as loose as a sieve. Government inspectors routinely foil the system, carrying on knives and guns and snooping around in secure areas.
Part of the problem is Americans themselves. They have proved to be an impatient lot - particularly as congestion has increased delays at the nation's airports. They value freedom, convenience, and low-cost flights - and increased security muscles in on all three of those priorities.
But a democracy must balance freedom and security, as Transportation Secretary Norman Mineta said Tuesday.
That balance has just been tipped. "There will be higher levels of surveillance, more-stringent searches," he said. "Travelers may experience some inconveniences.... But we must do whatever it takes, with safety as our highest priority."
That comes as a relief to at least one United Airlines pilot, who preferred that her name not be used. She and her colleagues routinely talk about the laxness of security at American airports, particularly compared with those in Europe and Israel.
"There are a lot of loopholes," she says. The main concerns, echoed by security experts, are the independent contractors who cater the planes and screen passengers at security checkpoints.
In a report issued last year, Congress's General Accounting Office (GAO) cited longstanding problems impairing the effectiveness of security screeners - a "key line of defense." Top among them, are inadequate training, high rates of turnover - as much as 400 percent a year - and low pay.
"We pay screeners lower salaries in many cases than the fast-food workers at the airports," says the GAO's John Anderson. "The system really gets down to the capability of the screeners, and that's something that people really need to rethink now."
According the Federal Aviation Administration, in 1978 screeners failed to detect 13 percent of illicit objects during compliance tests. Ten years later, they failed to detect 20 percent. In 1997, the FAA stopped releasing such figures, contending that they are "sensitive security information."
But a year ago in April and May, undercover GAO investigators carrying false credentials and declaring themselves armed law-enforcement officers were "100 percent successful" in penetrating secure areas without being challenged.
"There's clearly a security problem at America's airlines," says Aaron Gellman of Northwestern University's Transportation Center in Evanston, Ill.
Attorney General John Ashcroft said that on at least two of the planes hijacked Tuesday, the perpetrators were armed with knives and box cutters. It's unknown whether they slipped past screeners or were placed on the planes beforehand by allies employed at the airport.
Because of the close coordination of the hijackings, insiders on the ground likely played key roles, says terrorism expert Peter St. John at the University of Manitoba in Winnipeg.
While the country is still absorbing the shock of the attacks, many experts say one enduring change may be the public's attitude toward the inconveniences imposed by increased security.
"Part of the problem is that the public hasn't been willing to suffer the loss of freedom that would be necessary to really tighten security," says Richard Gritta, an aviation expert at the University of Portland in Oregon. "But the diabolical magnitude and the perfection with which this was executed might change that."
Other experts hope the tragedy will force Congress and the FAA to invest the money needed to keep a sustained focus on increased security. The greatest risk, they say, is that security will drop as a priority, as it has after past tragedies.
Mark Clayton in Boston contributed to this report.