Lawmakers are vowing an investigation into how Capitol police handled the violent breach at the US Capitol, questioning whether a lack of preparedness allowed the mob to occupy and vandalise the building.
Four people died, a woman who was shot and three other people who suffered "medical emergencies" related to the breach, Washington, DC, Police Chief Robert Contee said.
Police said 52 people were arrested as of Wednesday night, including 26 on the Capitol grounds. Fourteen police officers were injured, Contee said.
Both law enforcement and Trump supporters deployed chemical irritants during the hourslong occupation of the Capitol complex before it was cleared Wednesday evening by law enforcement.
Representatives Zoe Lofgren, a Californian Democrat and chairwoman of the House Administration Committee, said the breach "raises grave security concerns".
She said her committee would work with House and Senate leaders to review the police response - and its preparedness - to a violent mob loyal to President Donald Trump that stormed the Capitol and forced lawmakers into hiding.
The incident forced lawmakers to crouch under desks and don gas marks, while police futilely tried to barricade the building. A woman was shot and killed inside the Capitol, and Washington's mayor instituted an evening curfew in an attempt to contain the violence.
Representative. Val Demings, a Florida Democrat, a former police chief, said it was "painfully obvious" that Capitol police "were not prepared for today".
"I certainly thought that we would have had a stronger show of force, that there would have been steps taken in the very beginning to make sure that there was a designated area for the protesters in a safe distance from the Capitol."
Demings said it appeared police were woefully understaffed, adding that "it did not seem that they had a clear operational plan to really deal with" thousands of protesters who descended on the Capitol following Trump's complaints of a "rigged election."
The rioters were egged on by Trump, who has spent weeks falsely attacking the integrity of the election and had urged his supporters to come to Washington to protest Congress' formal approval of President-elect Joe Biden's victory.
The protests interrupted those proceedings for nearly seven hours.
The mob broke windows, entered both the Senate and House chambers and went into the offices of lawmakers, including House Speaker Nancy Pelosi.
Demings said there were "a lot of unanswered questions and I'm damn determined to get answers to those questions about what went wrong today."
Representative Karen Bass, a Californian Democrat, said she was outraged to see accounts on social media of a Capitol Police officer posing for a photo with a protester.
"Would you take a selfie with someone who was robbing a bank?"