Just days ahead of President-elect Joe Biden's inauguration, the entire country is on edge.
The FBI has warned of indications that "armed protests" are being planned at all 50 state capitols and the US Capitol in Washington in the days leading up to January 20. A joint bulletin from the Department of Homeland Security, the FBI and eight other agencies says domestic extremists pose the most likely threat to the presidential inauguration -- particularly those who believe the incoming administration is illegitimate.
"As somebody who worked on al Qaeda-related terrorism throughout the 2000s at the Justice Department and worked extensively on counterterrorism investigations and cases, there were several times where we were anticipating a follow-on attack to a world event," Carrie Cordero, a CNN legal and national security analyst, said Saturday. "I have that same feeling now."
"It feels like there is a substantial threat that exists," Cordero added.
In response, state leaders across the US are ramping up security around their capitol grounds -- pulling in National Guard members for help, erecting barriers, boarding up windows, asking residents to avoid the area and some even closing down capitol grounds altogether.
In Washington, DC, the Pentagon has authorized up to 25,000 National Guard members for Inauguration Day. National Guard members supporting US Capitol Security will be armed, according to the Department of Defense. The inauguration ceremony rehearsal will now be delayed a day amid heightened security concerns, acting Homeland Security Deputy Secretary Ken Cuccinelli said.
Cuccinelli cited "online chatter" about the previously scheduled rehearsal day on Sunday, but said there are "no specific credible threats."
"The decision was made to delay a day and leave the Secret Service in a position, and the whole team across the Washington metro area, to be prepared to respond on that day if needed," he said.
DC mayor urges Americans to watch inauguration from home
In a fortified Washington, DC, Mayor Muriel Bowser has urged Americans to enjoy the inauguration virtually from home and has asked anyone who does not need to be out to avoid restricted areas.
"Our goals right now are to encourage Americans to participate virtually and to protect the District of Columbia from a repeat of the violent insurrection experienced at the Capitol and its grounds on January 6," Bowser said during a news conference Monday.
On Friday, US Capitol Police arrested a Virginia man as he attempted to pass through a police checkpoint with unauthorized inaugural credentials, an unregistered handgun and more than 500 rounds of ammunition, according to court documents.
In an interview with the Washington Post, the man said he spent the past week working as hired security in Washington, DC, and had been given credentials to guard media equipment. He told the Post he had forgotten that he had his firearm in his car when he left his home in Virginia, where he said he had a license to carry.
USPS removes blue mailboxes
Ahead of Wednesday's ceremony, the US Postal Service (USPS) has temporarily removed some mailboxes in several major cities across the US as a security measure to protect postal property, employees and the public, according to news releases from USPS jurisdictions in at least 17 states.
Many USPS blue collection boxes in Washington, DC, will either be temporarily removed or locked and notices have been placed on the individual boxes indicating the date they will be unavailable for service.
The agency took the same measures in the nation's capital during President Donald Trump's inauguration four years ago.
The expansion to other locations, a spokesperson told CNN, is based on USPS' awareness of "planned protests or other situations involving large crowds" in key cities and areas.
TSA increases security posture
The Transportation Security Administration said Friday it has "significantly increased its security posture" following the Capitol attack and in preparation for the inauguration, adding it is processing "hundreds" of names with law enforcement agencies for risk assessment.
"Our intelligence and vetting professionals are working diligently around the clock to ensure those who may pose a threat to our aviation sector undergo enhanced screening or are prevented from boarding an aircraft," the agency said in a statement.
The agency said there are now additional layers of security at DC-area airports and other transportation hubs, including "more law enforcement and explosives detection canine teams" and random gate screening.
"Our workforce continues to coordinate closely with partners at the federal, state, and local level as well as appropriate intelligence communities to ensure TSA's posture over the coming days continues to incorporate all necessary security measures and capabilities within our authority," it added.
The House Oversight Committee also sent letters Thursday to more than two dozen operators of bus lines, rental car companies and hotels asking for assistance in "identifying and preventing the ongoing and extreme threat of further violent attacks in Washington, DC, and elsewhere over the coming days."
The request also noted the rioters from earlier this month "relied on a range of companies and services to get them there and house them once they arrived," and asked companies to increase security and screening of guests and keep business records available for future investigations.
'Nothing left undone': States closing, arming their capitols
Meanwhile, local and state leaders from coast to coast have boosted security for the coming days following officials' warnings of potentially more violence.
In Kentucky, Gov. Andy Beshear announced state capitol grounds will be closed entirely Sunday to "further ensure the safety of everyone -- both on or around the grounds and in the neighborhoods surrounding" the Capitol.
"Domestic terror is never OK," he said in a statement. "We must stop it every time we see it, and we cannot let what we saw at the U.S. Capitol become a new normal for this country."
Texas officials also said the state Capitol and its grounds will remain closed from Saturday to Wednesday, adding they were aware of "armed protests planned" and "violent extremists who may seek to exploit constitutionally protected events to conduct criminal acts."
Maryland Gov. Larry Hogan declared a state of emergency related to the inauguration, to allow the state to "more efficiently coordinate support and provide assistance" to its local jurisdictions and neighboring states, the governor's office said Friday.
Minnesota's leaders said Friday they're ready ahead of anticipated protests, noting there were no credible threats against the state Capitol.
"I want you all to be comfortable and assured that there has been nothing left undone to keep the capitol safe," Department of Public Safety Commissioner John Harrington said.
"We are not panicking," Lt. Gov. Peggy Flanagan added. "We are concerned, we are alert, and we are prepared."
In South Carolina, officials in the city of Columbia advised anyone who does not need to be in the city center, near the state's Capitol, to stay home.
"Unless there's a need, this weekend, and certainly on inauguration day, to be downtown," Mayor Stephen Benjamin said, "I encourage you to stay home."
CNN's Priscilla Alvarez, Greg Wallace, Lauren Fox, Hollie Silverman, Raja Razek, Ross Levitt, Artemis Moshtaghian, Manu Raju, Jamie Crawford and Whitney Wild, Jon Passantino, Rebekah Riess contributed to this report.