Former FBI boss James Comey has told Sky News he is worried about the threat of violence from “armed, disturbed people” at Joe Biden’s inauguration.
The new US president will be sworn on Wednesday amid high security after the FBI identified more than 200 people threatening violence in “concerning online chatter”.
Fuelled by unsubstantiated claims by Mr Trump, many of his supporters believe there was fraud in November’s election.
“I’m worried because there are armed, disturbed people who are in this state of mind where they believe their country is being taken from them,” said Mr Comey.
“So it’s a threat law enforcement in the States has to take very seriously.
“At the same time, I know that we have the capability, investigative and the tactical capability on scene, to protect these locations and so I am optimistic that the threat will be neutralised, but it has to be taken very, very seriously.”
The National Guard has been descending on Washington to guard government buildings ahead of inauguration day, when officials say 21,000 will be on hand.
The storming of the Capitol building – the heart of US Democracy – on 6 January caused widespread shock in America and across the world, with Trump supporters running amok and leaving five people dead.
Police were hugely outnumbered and have been criticised over how easy it was for the rioters to seize control.
Mr Comey told Sky News he was “sickened” by the violence and angry at the failure to defend the building, despite the obvious threat.
“I was angered by the apparent failure to defend a hill, it [the Capitol] sits on a hill with 2,000 officers assigned to it on a daily basis, the failure to defend the hill. It just mystifies and angers me,” he said.
“It is going to be important for our country to understand that failure.”
He added: “9/11 we were told was a failure of imagination, we didn’t anticipate the way the terrorists might come at us; this didn’t require imagination.
“This was all over the internet and the group literally walked slowly down Pennsylvania Avenue towards the Capitol so it was just a failure and we need to know why at all levels so that we don’t let it happen again.”
Mr Comey is a fierce critic of Mr Trump – who he has previously compared to a mafia boss.
He was fired by the president in May 2017 while the FBI was investigating Russian meddling in the 2016 presidential election.
White House officials accused him of mishandling the investigation into the email practices of Hillary Clinton, but Mr Trump later confirmed the “Russia thing” was on his mind when he made the decision.
Mr Comey, 60, has just released a new book called Saving Justice: Truth, Transparency, and Trust, described as a “clarion call for a return to fairness and equity in the law”.
The disgust among many Americans over the Capitol riots this week led Mr Trump to become the first president to be impeached twice after the House of Representatives charged him with inciting the riot.
No date has been set for the political trial that follows, where senators can also vote by a simple majority to block Mr Trump from ever standing for election again.
You can watch the full interview on Sophy Ridge on Sunday from 8.30am.