According to a letter cited by news outlets, Capitol Police Chief Steven Sund said he would resign on January 16.

Officers in the 2000-member Capitol Police fell back as crowds advanced on Wednesday, enabling Trump supporters angry about his election defeat to invade the halls of Congress to disrupt certification of Biden’s victory. Other officers fought to keep lawmakers and staff safe.

Capitol Police did not respond to inquiries about why they had not cordoned off the area or brought in more support officers ahead of the protests, which Trump himself urged to be “wild”.

Republican Senate Leader Mitch McConnell called the breach a “shocking failure”, while US House of Representatives Speaker Nancy Pelosi called for Sund’s resignation.

“He hasn’t even called us since this happened,” Pelosi said of Sund during a news conference on Thursday.

“Many of our Capitol Police just acted so bravely and with such concern for the staff, the members, for the Capitol … and they deserve our gratitude. But there was a failure at the top of the Capitol Police,” she said.

Pelosi also said that Paul Irving, the House sergeant-at-arms, would resign. Top Senate Democrat Chuck Schumer said he would fire Michael Stenger, the Senate sergeant-at-arms, as soon as runoff elections in Georgia for two seats are certified and Democrats control the Senate.

Trump supporters ransacked legislators’ offices, stole computers and documents, and left threatening messages as they roamed the building for hours in a rampage that left four people dead: one shot by police and three who died of medical emergencies.

Sedition charges being considered

Washington DC’s top federal prosecutor said those who took part in storming the Capitol could face charges of sedition, rioting or insurrection.

“We’re looking at all actors here and anyone that had a role, and the evidence fits the elements of a crime, they’re going to be charged,”Acting US Attorney Michael Sherwin said.

“We’re not going to keep anything out of our arsenal.”

Sherwin said the Justice Department had filed 55 criminal cases about events this week, – some pre-dating Wednesday’s assault on the seat of government – including the arrest of far-right Proud Boys leader Enrique Tarrio on Monday.

Sherwin repeatedly said no suspects in Wednesday’s riots would be ruled out – even when asked whether this could include Capitol Police who may have been complicit or Trump himself for urging protesters to march on the Capitol at a rally on Wednesday.

“We’re looking at all actors here and anyone that had a role, and the evidence fits the elements of a crime, they’re going to be charged.”

Police response to Trump versus Black Lives Matter protests called out

The crowd racing through the Capitol with Trump flags and his signature red hats stood in sharp contrast to the response to anti-racism protests this summer.

At that time, the White House was surrounded by multiple blocks of buffer, and law enforcement officers used tear gas, projectiles and at one point the downward blast of a helicopter rotor to push back protesters.

In comparison, the streets around the Capitol were open on Wednesday morning, and scatterings of Capitol Police stood at low metal barriers resembling bicycle racks.

District Councilman Charles Allen, who represents the area around Capitol Hill, called that contrast particularly jarring.

“They were overrun and, in many cases, appear to have completely opened the gates, snapped selfies,” Allen said. “By the time they called D.C. Metropolitan Police Department, it was too late.”

House Appropriations Committee Chairwoman Rosa DeLauro and Representative Tim Ryan, who is leading a probe, said in a statement: “There was a severe systemic failure in securing the building’s perimeter and in the response once the building was breached.”

A House Democratic aide, speaking on condition of anonymity, said the investigation would focus on what intelligence was available in the run-up to the riot, how decisions were made and why the perimeter of the Capitol was not more secure.

The aide said that some protesters were found carrying zip ties. Those heavy-duty plastic ties are often used to handcuff people, and could indicate an intent to kidnap members of Congress.

Pelosi joined dozens of House members in the safe room where they sheltered after protesters battered the doors of their chamber late on Wednesday, and told them she had received a steady stream of calls asking why reinforcements had not been dispatched more quickly.

“Why are they not coming now? Almost a constant flow of calls,” Pelosi said. “That is something to review.”

Pelosi and other lawmakers also praised the Capitol Police for protecting their staff and journalists. Many officers were injured.

-with AAP