Associated Press
A TSA agent performs an enhanced pat-down on a traveler at a security area at Denver International Airport.

How did an agency created to protect the public become the target of so much public scorn?

After nine years of funneling travelers into ever longer lines with orders to have shoes off, sippy cups empty and laptops out for inspection, the most surprising thing about increasingly heated frustration with the federal Transportation Security Administration may be that it took so long to boil over.

The agency, a marvel of nearly instant government when it was launched in the fearful months following the 9/11 terror attacks, started out with a strong measure of public goodwill. Americans wanted the assurance of safety when they boarded planes and entrusted the government with the responsibility.

But in episode after episode since then, the TSA has demonstrated a knack for ignoring the basics of customer relations, while struggling with what experts say is an all but impossible task. It must stand as the last line against unknown terror, yet somehow do so without treating everyone from frequent business travelers to the family heading home to visit grandma as a potential terrorist.

The TSA "is not a flier-centered system. It's a terrorist-centered system and the travelers get caught in it," said Paul Light, a professor of public service at New York University who has tracked the agency's effectiveness since it's creation.

That built-in conflict is at the heart of a growing backlash against the TSA for ordering travelers to step before a full-body scanner that sees through their clothing, undergo a potentially invasive pat-down or not fly at all.

"After 9/11 people were scared and when people are scared they'll do anything for someone who will make them less scared," said Bruce Schneier, a Minneapolis security technology expert who has long been critical of the TSA. "But ... this is particularly invasive. It's strip-searching. It's body groping. As abhorrent goes, this pegs it."

A traveler in San Diego, John Tyner, has become an Internet hero after resisting both the scan and the pat-down, telling a TSA screener: "If you touch my junk, I'm gonna have you arrested." That has helped ignite a campaign urging people to refuse such searches on Nov. 24, which immediately precedes Thanksgiving and is one of the year's busiest travel days.

The outcry, though, "is symptomatic of a bigger issue," said Geoff Freeman, executive vice president of the U.S. Travel Association, an industry group that says it has received nearly 1,000 calls and e-mails from consumers about the new policy in the last week.

"It's almost as if it's a tipping point," Freeman said. "What we've heard from travelers time and again is that there must be a better way."

Indeed, TSA has a history of stirring public irritation. There was the time in 2004 when Sen. Ted Kennedy complained after being stopped five times while trying to board planes because a name similar to his appeared on the agency's no-fly list. And the time in 2006 when a Maine woman went public with her tale of being ordered by a TSA agent to dump the gel packs she was using to cool bags of breast milk. And the time in 2007, when a Washington, D.C. woman charged that another TSA agent threatened to have her arrested for spilling water out of her child's sippy cup.

After Congress approved creation of the agency in late 2001, the TSA grew quickly from just 13 employees in January 2002 to 65,000 a year later. In the first year, agency workers confiscated more than 4.8 million firearms, knives and other prohibited items, according to a report by the U.S. Government Accountability Office.

But even as the new agency mushroomed, officials at the top, pressured by airlines worried that tighter security would discourage people from flying, looked to the business world for lessons on systems, efficiency and service.

TSA set up "go teams" pairing government employees with executives from companies including Marriott International Inc., The Walt Disney Co., and Intel Corp., to figure out how to move lines of people through checkpoints efficiently and how to deal with angry travelers.

But the agency was working under what Freeman calls "an unachievable mandate." Congress demanded an agency that eliminated risk. But the risks are always changing, as terrorists devise new methods and government parries. That has led to an agency that is always in crisis mode, constantly adding new policies designed to respond to the last terror plot.