In a statement, Senate majority leader Mitch McConnell said on Thursday that an investigation into what went wrong, as well as a wider Capitol security review, would now be carried-out.
Bi-partisan committees and congressional leaders were already in initial discussions, said Mr McConnell, who labelled Wednesday’s scenes as “shocking”.
She was speaking a day after one woman was shot as the Capitol was besieged by rioters who alleged the 2020 election was “rigged” against the US president.
His supporters scaled walls, stormed the Senate chamber, smashed windows and planted two explosives - and delayed the confirmation of Joe Biden’s presidential win in the process.
In his statement, the Senate leader said: “Yesterday represented a massive failure of institutions, protocols, and planning that are supposed to protect the first branch of our federal government”.
“A painstaking investigation and thorough review must now take place and significant changes must follow,” he continued.
The Republican went on to attack the US president, saying “unhinged criminals” had “tried to disrupt our democracy”, and that “those who incident them” were responsible.
“Congress is also deeply grateful to the local officers from D.C., Virginia, and Maryland, the federal law enforcement personnel, the National Guard, and all the other professionals who deployed to help subdue the criminals and retake the Capitol,” Mr McConnell added.
Muriel Bowser, who had requested the state troops from Virginia and Maryland to assist Washington DC, said at her own press conference on Thursday that there was “obviously a failure” within the Capitol’s security.
“Obviously it was a failure or you wouldn’t have had police lines breached and people entering the Capitol building by breaking windows and terrorising people,” said Ms Bowser.
“Clearly, there was a failure there. There’s got to be a real investigation into what happened,” she added.
Ms Bowser, who drew comparisons with the militarised response to Black Lives Matter demonstrations in the city last year, said that disparity should also be investigated.
Footage from Wednesday showed crowds easily overwhelm Capitol police lines to enter Congress, while those who demonstrated last summer were met more forcefully.
Following the incident, the National Guard will now construct a seven-foot fence around the Capitol, which will be in place for a month, according to Ms Bowser’s press conference.
The mayor, who ordered an overnight curfew on Wednesday, has since declared an emergency that will last for 15 days.
Defending his officers’ response, Capitol Police chief Steven Sund said rioters "actively attacked" Capitol police, who "acted valiantly when faced with thousands of individuals involved in violent riotous actions."
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