WASHINGTON They are screened so carefully that their families are interviewed before they are hired. They hold top-secret security clearances, are trained to use lethal force and stand inches from the leader of the world's most powerful nation.
U.S. Secret Service agents are also drilled almost from Day One on the need for probity, discretion and solid morals.
"You will be exposed to so many new experiences, challenges and, yes, temptations - a Secret Service agent can sometimes be perceived as celebrity. We are not," a top official warned a 2002 graduating class of agents.
The self-image of the Secret Service's proud, but insular, culture has been challenged like at no time in modern history by allegations that agents took prostitutes back to their hotel rooms in Cartagena, Colombia, last week on the eve of President Barack Obama's arrival for a hemispheric summit.
Six employees, including two supervisors, have either resigned, retired, or been proposed for firing. On Friday, the Secret Service said a 12th employee had been implicated, placed on administrative leave and stripped of his security clearance.
The question now is whether what happened in Cartagena was an isolated incident, the actions of agents who failed the Service's high standards - or something more systemic in a 146-year-old agency first founded to combat counterfeiting.
'NOT A SYSTEMIC SORT OF THING'
Former top Secret Service officials, and the agency's many defenders, insist that the scandal is both unprecedented and no reflection of the Secret Service as a whole.
There have been individual instances of Secret Service employees caught in "difficult" situations in the past, but nothing on this scale, said Ralph Basham, a former Secret Service director.
"But it's not a systemic sort of thing. It's not a fiber that's woven through the fabric of the organization. Generally it's individuals who just do something stupid and get themselves in trouble," he said.
The Colombia incident was an anomaly, Basham said. "The sheer number of people who decided to engage in this, that's what is shocking."
Secret Service Director Mark Sullivan, a 29-year veteran, has so far won plaudits from U.S. lawmakers for quickly launching an investigation and being transparent about the agency's handling of the scandal.
And, so far, no recent incidents of similar misbehavior have surfaced publicly, reinforcing those like Basham who say Cartagena was extremely unusual.
The Service's defenders are quick to point out that the employees under investigation were not members of the presidential protective detail. Those are the agents considered the cream of the agency who stick close to the president when he travels, watch crowds from behind dark sunglasses, and have suits fitted so they hide their weapons.
Those in Cartagena, which included members of the less-elite Uniformed Division -- who operate metal detectors and stand guard at various posts on site -- were support personnel who came over on the plane to Colombia that brought the president's armored vehicles.
And yet, two of them were not rank-and-file employees, but supervisors.
But to critics and the public such distinctions may be too fine a point, and the image of government agents gone wild in a foreign land threatens to tarnish the agency, with Secret Service already turning into a double meaning for racy jokes.
The 2002 graduates were lectured by a top agency official that "your daily conduct must be better than that which is technically legal - your compass must point to that which is right with a clarity and precision that reflects your commitment to this new responsibility." The statement, from a document released in 2007 under the Freedom of Information Act, provides a glimpse into how the agency's newest members start their careers.
Secret Service agents at work in public are generally seen but not heard. Their physical presence is quite visible around the president ready to shield him from any threat, but they tend not to draw attention to themselves as individuals.
The Colombia incident has revealed that after hours, not all Secret Service employees practice discretion.
A woman in Cartagena said she met American men in a salsa bar the night of the incident who bragged "we're the bodyguards of the most powerful man in the world." She said she did not accompany them back to a hotel.
David Chaney, a Secret Service supervisor who was allowed to retire over the incident, posted photos of himself protecting former Republican vice presidential candidate Sarah Palin on his personal Facebook page. He included this comment: "I was really checking her out, if you know what i mean?"
"That really bothered me. And I'm no moralist. But ... when it's your job to be protecting someone, especially when that person is a female, to be making those types of remarks and be posting them, is absolutely indefensible," Representative Peter King, chairman of the House Homeland Security Committee, told CNN.
Chaney's Facebook site also shows connections in many cities, many of them young women, including flight attendants and university students.
Among his 391 "friends" is a blonde in a provocative pose who boasts: "I party like a rock star, look like a movie star, play like an all star ... BABY I'M A SUPERSTAR." Her page, which also includes a vulgarity, links to a pornographic web site.
The Secret Service has long been proud that its agents are ready to face danger at any moment - to take the proverbial bullet intended for the President.
It is more than mere bluster.
One agent died in the failed assassination attempt on President Harry Truman. Another was wounded shielding President Ronald Reagan in a 1981 assassination attempt. After President John F. Kennedy was fatally shot, an agent flung himself onto the car in which they were riding and shielded the president and first lady with his body.
The agency protects the president and vice president and their families, as well as visiting foreign dignitaries. No president has been "lost" under their watch since the 1963 assassination of President Kennedy.
Yet behind the impassive visage of Secret Service officers sometimes lies the fallout from intense stress; mind-numbing boredom of long, event-free shifts; and family stress due to dedication to the agency and unpredictable travel schedules.
"Fatigue, stress, fear, domestic woes, alcohol and drug abuse, and every frailty of human nature permeate the Secret Service, and though the bulk of the force either rises above or tamps down the pressures, many agents battle a range of demons from the bottle to burnout," Philip H. Melanson wrote in "The Secret Service: The Hidden History of an Enigmatic Agency."
In February 2002 some of Vice President Dick Cheney's agents wrapped up their shift in San Diego, went to a local watering hole, and tossed down some beers, Melanson recounted. "Many drinks later," the book says, four agents were in a melee with 15 civilians, one of whom later admitted to trying to take an agent's gun. The agent then allegedly bit part of his ear off.
After the September 11, 2001 terrorist attacks, the Secret Service faced stress of another kind, as its missions expanded.
Yet if the Secret Service needs testimony that events like Cartagena are indeed an exception, it has the best possible witnesses: those it has protected.
"I think the Secret Service are outstanding. They did a brilliant job taking care of me and my family," said Senator John Kerry, a former Democratic candidate for president.
"Maybe some few people made a terrible mistake," Kerry said. "I have nothing but praise for the Secret Service. And I think this is not characteristic of the Secret Service I know."
(Additional reporting by Susan Cornwell in Washington, Mario Naranjo and Helen Murphy in Cartagena; Editing by Lisa Shumaker)