Washington, D.C. is taking a defensive posture in the lead-up to Inauguration Day. Some 25,000 National Guard troops have been OK'd to descend on the city at the behest of the Secret Service. 

Here's everything you need to know about the city's security plan: 

Secret Service leads in security details 

Every year, the Presidential Inauguration is designated a recurring National Special Security Event (NSSE). When an event is given this designation, the Secret Service becomes the lead federal agency responsible for coordinating security for the event. 

Matt Miller, the special agent in charge of the Secret Service, said the city has extended the special designation for security from Jan. 13 to Jan. 21, the day after President-elect Joe Biden is sworn in. 

The agency has called in reinforcements in the form of 25,000 National Guard members to assist in securing the downtown region of the city. 

Members of the National Guard patrol outside the Capitol Building on Capitol Hill in Washington, Thursday, Jan. 14, 2021. (Associated Press)

In addition to Capitol Police, thousands of local law enforcement officials from different states will provide back up to D.C. police, and hundreds of FBI agents are expected to be on the ground as well. 

The Federal Emergency Management Agency has also deployed resources to D.C. and the surrounding areas in Maryland and Virginia, said Maryann Tierney, a regional administrator. 

Ambulances will be prestaged close to the Capitol, and food and water sources will also be brought in closer to the district if they are needed. 

Double threat: Coronavirus pandemic and violent extremists 

The 59th Presidential Inauguration to swear in Biden has faced unique hurdles due to the coronavirus pandemic, as well as the heightened security threat after a riot on the nation's Capitol earlier this month left five people dead. 

Even before that, Biden's inaugural committee encouraged supporters to celebrate from the comfort of their home, as the team made provisions to have live streams and virtual celebrations to keep onlookers to a minimum and prevent the further spread of the virus. 

President-elect Joe Biden receives his second dose of the coronavirus vaccine at ChristianaCare Christiana Hospital in Newark, Del., Monday, Jan. 11, 2021. (Associated Press)

The FBI is now warning that agents have seen "chatter" constituting a credible threat from protesters intent on instigating a "war" in Washington, D.C.

City officials are erecting a perimeter throughout downtown, putting up barriers around the White House, the National Mall and the Capitol. In order to travel through the perimeter, people will need to provide proof of essential purpose.

The National Mall will be closed until after the inauguration and permits for gatherings have been suspended, with the exception of two designated areas -- at the Navy Memorial and John Marshall Park -- that will accommodate about 100 protesters on the day of the event.

Road closures and transit disruptions

D.C. Mayor Muriel Bowser announced that the city's Metro has closed 13 of its stations as well as four major bridges. Transit lines, including trains and buses, will be suspended and wide swaths of streets in and around the Capitol will be closed off. 

District of Columbia Mayor Muriel Bowser speaks during a news conference in Washington, Wednesday, Nov. 4, 2020. (Associated Press)

Statehouses at risk 

Statehouses around the country -- many of which have faced sometimes violent protests -- are also facing heightened security risks. 

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Dozens of state leaders have activated National Guard troops to provide backup to local law enforcement in days before the transition of power.