A counterterrorism expert says the mood in the United States following this month's Capitol riot is similar to that of the aftermath of 9/11 and described the significance of the FBI's warning of nationwide armed protests.
At least five people were killed during chaos in Washington DC on January 6 when pro-Donald Trump insurrectionists stormed Capitol Hill, desecrated the historic building, threatened to kill the vice-President and forced the evacuation of lawmakers. It followed a Trump rally, where the President called on his supporters to "fight" and march on the Capitol.
Since the siege, there has been heightened security across the United States, with the Capitol currently surrounded by barriers and thousands of National Guard members. The sense of anxiety was underscored on Tuesday morning when a small fire on a nearby highway led authorities to lock the Capitol down out of caution.
Speaking to The AM Show from Michigan on Tuesday, Javed Ali, a former senior director at the US National Security Council, said the mood was similar to that of the nation after 9/11, when terrorist attacks by al-Qaeda killed nearly 3000 Americans.
"I wouldn't say I am nervous. But I think the country is going through a very tense time. It seems, nationally, there is the same sense of anxiety and fear and dread that we had in those early days and weeks after 9/11," Ali said.
The key difference, Ali said, was that the current threat is not from a foreign country.
"What I find so remarkable, if that comparison is accurate, is that we are not dealing with a foreign-based threat of individuals trained in al-Qaeda camps deploying into the United States to conduct the attacks like we had on 9/11," he told The AM Show.
"We are talking about Americans born and raised here who are not buying into a foreign ideology, but a very domestic, American one and present a different kind of terrorism challenge and problem. The paradigm has shifted, but at least the mood within the country seems to be roughly the same from almost 20 years ago."
All eyes are now on Joe Biden's inauguration on January 20, with 20,000 National Guard troops expected to be present.
There have been reports - including from the Associated Press - that US Defence officials are worried about an insider attack or another threat from those working to secure the inauguration. That's prompted the FBI to vet all of the incoming troops.
However, on Tuesday morning, Acting Secretary of Defence Chris Miller said there was "no intelligence indicating an insider threat".
Ali, who has worked at the Department of Homeland Security and the FBI, said he wouldn't be "overly alarmed" at the vetting process, describing it as "prudent". If there was a threat, any potential perpetrators would be flown back to base or arrested, he said.
"That is actually relatively routine, if not normal, in these kinds of situations."
While the main focus is on Washington DC, another question is whether attacks could be planned somewhere else in the United States. Ali said that is definitely something that will be considered by authorities.
"No matter what you do on the government's side to plan, prepare and even to respond… people who are mobilised to violence or violent action, they can shift to other potential targets based on their knowledge of potential vulnerabilities elsewhere."
He mentioned an internal FBI bulletin, of which details were released last week. It warned of armed groups planning protests at all 50 state capitals between January 16 and January 20, and at the US Capitol between January 17 and 20.
Such a nationwide bulletin was significant, Ali told The AM Show.
"Having worked at Homeland Security and then the FBI in the 2000s, and knowing exactly what goes into these kinds of bulletins and warnings, at least in my recollection, on the federal government side, there hasn't been a nationwide warning like that, about a potential threat that could appear anywhere, in almost 20 years since the stand up of Homeland Security in the early 2000s.
"When the Government sends these messages out, they are very rare with that kind of nationwide potential for terrorist or extremist violence."
Ali believes the threat will endure for a long period of time and one of the biggest challenges for authorities will be deciding how long they can maintain the current level of security.