The Inauguration won't just be the biggest day in Donald Trump's life. It may also be his most dangerous. So what's it like to keep a president safe on his first day in office?
Former Secret Service agent Dan Bongino knows first-hand. He walked alongside President Barack Obama's Inaugural parade eight years ago.
"I was the lead advance agent for the zone where he got out of the vehicle to wave. It was a big responsibility. It was one of my prouder moments as a Secret Service agent," Bongino said.
And when it's the newly-inaugurated President Trump's turn to roll down Pennsylvania Avenue on Friday afternoon, his security detail will be prepared for the worst.
"Protecting the president on Inauguration Day, you have to view it through the Secret Service model, what we would call the big six: Tactical threats, biological threats, chemical-biological threats, [improvised explosive devices], airborne attacks, and fire/geological stuff," said Bongino.
The president's limo, nicknamed "The Beast," is designed to withstand such catastrophic attacks. But what'll the Secret Service look for if Trump, like nearly every president for the last 40 years, decides to get out of the car and walk a few blocks?
"There are so many places. We have to worry about a potential sniper round being fired from anywhere in D.C. You have to remember as a Secret Service agent, you have to make every step, every patch of concrete the president steps on as safe as the residence of the White House. Now when you're talking about an entire city of Washington, DC, that's not easy to do," he said.
After leaving the Secret Service, Bongino became a conservative commentator and has made three unsuccessful runs for Congress. But when it comes to serving the brand-new president, he said duty knows no party.
"Protecting the president especially on Inauguration Day, where you have a new president, reinvigorated sense of energy in the country, it's the most solemn responsibility a federal law enforcement officer can have."
