Nate Burleson, formerly a wide receiver in the NFL, is co-host of "CBS Mornings."

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As a former NFL player, I thought I knew what it meant to be tested. But after spending a day with the U.S. Secret Service's Counter Assault Team in Laurel, Maryland, I found out what it takes to make one of the most exclusive teams in national security.

Created in 1865 by the Treasury Department to combat currency counterfeiting, the Secret Service expanded its role after the assassination of President William McKinley in 1901. Today, it boasts more than 7,000 people who quietly ensure the safety of the American president, vice president, visiting world leaders and its financial system.

Secret Service director Kimberly Cheatle, who has experienced the demands of the job firsthand, served on the protective detail of Vice President Dick Cheney during 9/11 and was part of the team safeguarding then Vice President Joe Biden during the Obama administration.

She said the agency's successes "99.9% of the time are never talked about."

"We are just the silent success in the background of history," she said.

On a sweltering day in Maryland, the task at hand was understanding the try-out process for special agents aspiring to join the CAT team, as the Counter Assault Team is known. Instructors like Jay Randol, with nearly 30 years of Secret Service experience, play a crucial role in shaping the elite agents — and if you want to make the CAT team, you likely have to go through him.

With temperatures soaring to nearly 107 degrees, I was feeling the heat. Randol said for testing, agents are put under physical duress.

"It's not an issue of: Can you do it? A lot of these guys ... can do it. Dry, flat range, everything perfect, cool conditions. But can you do it on fire? Can you do it in the moment? Can you do it when you've had your behind handed to you?" he said.

We worked with live firearms, a reminder of the power of the weapons. Gun safety was constantly stressed.

After a quick break involving some much-needed hydration, I resumed the fitness test, pulling 100-pound sleds, doing tire flips and carrying kettlebells up six stories — tasks meant to test physical and mental limits.

The Secret Service needs to make sure all special agents who are responsible for protecting the President of the United States can execute their duties even while under extreme exhaustion. Carrying the kettlebells nearly broke me down, along with my photographer Kenton Young, who was running alongside me the entire time.

The climax of the day featured a real-time simulation of a presidential motorcade under attack, where I applied my newfound training to neutralize the targets.

Special agent Jamar Newsome, who is also a former NFL wide receiver, likened it to football reps.

"That's the only way to get good at it," he said. "If you don't practice it, you're never gonna get good at it."

The Secret Service showed that day that they can execute with no margin for error.

Cheatle said that "a quiet day on the books is a good day."

"We like to say we are quietly in the background and successful and nobody hears about us, and that means it was a good day," she said.

Nate Burleson

Nate Burleson is a co-host of "CBS Mornings."

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