Inside the Massive Inauguration Security Effort

— -- As thousands of people descend on Washington D.C. for the inauguration of President-elect Donald Trump, months of security planning, intelligence gathering and coordination are coming to fruition to protect lawmakers and the public.

The event, like the pope’s visit and the Democratic and Republican national conventions, is designated as a national security event, which unlocks federal resources and allows Secret Service to assume the leadership role for security.

While there are no specific or credible threats, almost every federal partner imaginable will be contributing to the security apparatus this weekend, including the FBI, ATF, Park Police, Customs and Border Protection, the Coast Guard, Centers for Disease Control and Prevention and the Department of Energy.

The United States Capitol Police Department is responsible for securing the Capitol and the Metropolitan Police Department will be primarily protecting the parade route, while still serving the entire city outside of inaugural activities.

In addition, more than 3,000 police officers from around the country are expected and National Guard troops will be patrolling.

The Planning

The planning process has been going on for well over a year, with various agencies holding tabletop exercises, coordination drills and working to staff the massive security undertaking.

The Secret Service trained for nearly every contingency. In a simulation, agents practiced how they would handle a drone spraying weaponized gas on the president and the crowd, a suicide vehicle attack as well as administering first aid if the president himself is attacked.

“Our number one concern is to keep our protectees and the general public safe and secure during all the inauguration events,” said Brian Ebert, Secret Service Special Agent in Charge.

Customs and Border Protection (CBP), which will be contributing to air support on Inauguration Day, did test runs around Washington, D.C. in the week leading up to the event to make sure communication systems were functioning.

“With the heightened awareness -– the possible threats -– we just want to do everything we can to put a stop to that,” a CBP pilot told ABC News' Senior Justice Correspondent Pierre Thomas on one of the test flights in a AS350 A-Star helicopter.

The Metropolitan Police Department (MPD) sent personnel to the Democratic and Republican national conventions last year to study the security procedures there, as well studying local demonstrations in Washington, D.C. to prepare for the rallies expected this weekend, some of which has already taken place throughout the city.

“We expect by and large, people come here to exercise their First Amendment rights, that's what Washington, D.C. is all about. In the event we have a few that want to create problems, if they break the law, we'll be able to handle that as well,” said MPD interim Police Chief Peter Newsham.

He added that if something happens in D.C., “it won't be for a lack of planning.”

Security Measures

Law enforcement sources from across government told ABC News that they are utilizing a “multi-layered” approach to security.

There will be visible layers, like physical barriers, checkpoints with magnetometers, bag searches and patrolling uniformed officers, as well as hidden layers, such as plainclothes officers inside and outside of the perimeter, radiation detection and surveillance cameras.

"We talk through and identify and gaps in our training or in our communications. So we plan for those up front. On game day, it is seamless, and that is so important, because real-time information is where it's at," said Park Police Chief Robert MacLean.

Major roads, tunnels and bridges leading to the Capitol and downtown D.C. will be closed.

To protect against a possible vehicle attack, like those that have happened recently in Germany and France, trucks filled with sand will be deployed to block the parade perimeter.

CBP helicopters will be scanning the city tomorrow, looking for any possible threats and will be in direct contact with the Secret Service Command Center.

On the Potomac River, Coast Guard cutters will be patrolling the waters and shoreline.

“There's lots of water that runs in or near the nation's capital. It's kind of a threat that's not well-known, but one that has to be protected,” said Coast Guard Capt. Lonnie P Harrison Jr.

Due to the forecast of rain tomorrow, the National Park Service today revised its “no umbrella” policy. "Totes"-style umbrellas that collapse will be allowed on the parade route as well as the National Mall for the inauguration, according to NPS. However, long, non-collapsible umbrellas will not be allowed. All umbrellas are still banned from the U.S. Capitol.

Potential Threats

The FBI and local law enforcement say there are no known, credible threats to the inaugural activities at this time, according to the FBI and local law enforcement.

However, security chiefs are adapting to the ever-evolving global threat environment.

The “lone-wolf threat is “very high among our concerns,” said Assistant Director in Charge of the FBI Washington Field Office Paul Abbate in an interview with ABC News.

These are people who are by definition, operating alone and often don’t pop up on the radar of law enforcement until it’s too late.

Over the past couple of years, there have been more and more actors inspired by larger terrorist organizations, like ISIS, but not directly connected to them.

“We're on the lookout for that each and every day,” said Abbate.

Law enforcement officers urge the public to remain vigilant and report anything suspicious, whether it’s an unidentified package or a person’s behavior.

Jack Date contributed to this story.