The former FBI director said there were “armed, disturbed people” who police would need to take seriously ahead of Wednesday’s event at the Capitol.
Thousands of armed National Guard troops are on the streets of Washington DC in preparation for expected protests by supporters of Donald Trump who believe his false claims of electoral fraud.
On Friday, a man was arrested at a security checkpoint in the city after police said he was carrying a fake inauguration pass as well as a loaded handgun and more than 500 rounds of ammunition.
Bridges into the city were to be closed, and the National Mall and other landmarks blocked off.
Speaking to Sky News’ Sophy Ridge on Sunday programme, Mr Comey said: “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 and so it’s a threat law enforcement in the States has to take very seriously.”
The unprecedented security operations across swathes of central Washington DC follows the attack on the Capitol building by pro-Trump demonstrators earlier this month.
Asked whether that violence was a failure by police, he said: “Yep, it seems that way to me. Watching it I was – as an American, as a human being – sickened by what I was watching.
"As someone who has spent a lot of my life in law enforcement, I was angered by the apparent failure to defend a hill, it 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. It is going to be important for our country to understand that failure.”
Asked whether he would like to see Mr Trump impeached, Mr Comey said: “I would. I think there has to be historic sanction for this behaviour.
"It is a close question as to whether he should be prosecuted after he leaves office, I am actually of the view that the country will be better off if we didn’t give him the platform that a prosecution would."
Describing the outgoing president as a “demagogue” and “mob boss”, he said he wanted to see Mr Trump shouting at cars from his lawn rather than given a high profile criminal trial that could keep him in the public eye for years to come.
“The country needs to find a way to heal itself and the new president needs the opportunity to lead and to heal us, as I said, both literally and spiritually and that will be much, much harder if the Donald Trump Show is on our television screens every single day in the nations’ Capitol," Mr Comey said.
"I’d like to see some of the lights go out and he can stand on the front lawn at Mar-a-Lago and shout at cars in his bathrobe and none of us will hear it.”
He also described Boris Johnson as “a little less crazy, a little less mean Donald Trump” when asked if Mr Biden will get on with the UK prime minister.
“I don't know Boris Johnson well enough to know. I gather he’s … at least he’s portrayed in the States as a little less crazy, a little less mean Donald Trump but I don't know whether that’s true or not.”