The Secret Service, which has been offering protection to presidents since 1902, has long enjoyed one of the most sterling reputations of any government agency.

That reputation has been tarnished by allegations that agents hired prostitutes in Colombia in advance of President Obama's trip there.

"The Secret Service episode is very sad," Ari Fleischer, who was White House press secretary under President George W. Bush, wrote Monday on Twitter. "I've always known the men & women of USSS to be the best, most professional ppl around."

To get a sense of who the members of the Secret Service are and what roles they typically play when a president travels overseas, NPR spoke with Jeffrey Robinson.

Robinson is co-author of Standing Next to History: An Agent's Life Inside the Secret Service, with Joseph Petro, a former assistant special agent in charge of the Secret Service's Presidential Protection Division (PPD).

NPR: Is there a typical sort of person who goes to work for the Secret Service?

Robinson: One of the things the Secret Service does is recruit both out of college and universities, and out of law enforcement. And what they're looking for is a pretty specific type of person. They generally like athletes, both men and women, because athletes understand working in a team situation.

You find a lot of Secret Service agents played football. In part, it's size, but football players understand positions and how to play that position in relation to other players playing other positions.

NPR: Your book opens with an anecdote about President Reagan deciding to throw out the first pitch at a Baltimore Orioles game, and that decision immediately putting 100 people to work to make it happen. How many people are involved when a president travels, particularly overseas?

Robinson: The president often travels with anywhere from 800 to 1,200 people. The Secret Service is always there in number. After all, you've got to have presidential protection 24 hours a day, which means three shifts, but then with time off you've got to have a fourth shift.

And then you've got all the support people. You've got the people running the metal detectors, the sniffer dogs; you've got people standing post, which means they surround several blocks; and then you've got that inner ring of security.

These people also have to eat. It's a very big operation. When the president moves, it is a circus.

NPR: How far in advance of a presidential trip does the Secret Service begin planning?

Robinson: The Secret Service goes everywhere the president will go. The Air Force gets involved, because Air Force One won't land anywhere the pilot hasn't practiced landing.

Three months before the trip, the Secret Service will meet with local police. About a month later, in something called the pre-advance, they'll go over contingencies. How many agents are we going to need? Is there an alternative route in and out of the airport?

Those agents who got in trouble in Cartagena were part of this team that moves in sometime before the actual visit to set up support for the Presidential Protective Division and the president's visit.

NPR: I want to ask you about that, but how much expertise does the Secret Service have about the various host countries when the president travels?

Robinson: They not only know 110 percent about every place where they're going, but they go there first to make sure. They walk it, they go into the hotels, they secure the hotels, they make sure the food is right. Nobody gets in or out without the Secret Service approval.

They know absolutely everything they're doing, and they have to because in the end, the life of the president [is] at stake. They go down to all the minute details so that nothing is left to chance. The president doesn't go anywhere, walk, sleep or eat anything that the Secret Service hasn't controlled.

They can't test the food served to the president. You can't have a taster, like for kings, to make sure the food is not poisoned. When I was living in England and various presidents visited and there were huge banquets at Buckingham Palace, the president would eat exactly what the queen of England ate, except the Secret Service would prepare it and the Secret Service would buy the ingredients. It looked the same — no one knew — but the Secret Service controlled the food.

NPR: Let's talk about this incident in Cartagena. How big a black eye do you think it will be for the Secret Service?

Robinson: The president's security was never once breached. But it damaged the pride of the Secret Service.

The Secret Service are really the best of the best. They're a great bunch of men and women, and one of the things you find when you meet a Secret Service agent is enormous pride in the service. They really are proud of the service in the same way that Marines are proud of the Marine Corps. There's that esprit de corps.

I know there are Secret Service agents all over the country who are furious at these 11 guys for tarnishing that reputation, and that, I think, is the biggest harm done — it tarnishes the reputation of an otherwise fantastic bunch of men and women.

NPR: You say the president's security was never breached, yet Rep. Darrell Issa, the California Republican who chairs the House Oversight Committee, and others have warned that this type of thing could lead to blackmail, which could endanger the president.

Robinson: These people were support staff. Most of them, I suspect, either had to do with the sniffer dogs or had to do with the metal detectors. They were nowhere near the president.

They risked the same kinds of problems that any businessman on a foreign trip would risk with a prostitute. They risked having their ID stolen, they risked violence, being set up. In the case of these agents, they have Secret Service identity which could be stolen, they have weapons which could have been stolen, so there is a real problem there.

Those agents probably do not have a career left and will be looking for work within the hour, and whatever happened will not happen again for a very long time.

But at no point does it jeopardize the president's security. Absolutely not.

NPR: But now we're hearing talk about "wheels up" parties that take place after a president departs the country.

Robinson: I don't see why they shouldn't have a party after wheels are up. They've done their job, they've worked very hard in a very concentrated way for a period of time, and they want to kick back. That's only normal. They may even sit there and have a bottle of beer like the secretary of state.

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