How a ragtag mob egged on by Donald Trump managed to overpower security and invade the US Congress triggered anger and disbelief in Washington on Thursday.
The debacle forced the resignations late on Thursday of Capitol Police chief Steven Sund and the top security officials of the two chambers of Congress, the sergeants-at-arms.
As dust settled on the extraordinary scenes of a besieged seat of power, voices were quickly raised to ask why the 2,300-strong Capitol Police force so easily gave way to protesters, appearing not to try to arrest them.
And the ease with which they breached security barriers to rampage through the white-domed building at the centre of Washington -- terrorizing lawmakers and briefly shutting down Congress -- laid bare a serious security threat two weeks before President-elect Joe Biden's inauguration.
Top lawmakers in the House and Senate demanded investigations into the breach, saying it exposed a weakness that should not be have been there since the September 11, 2001 attacks.
"It was well known that extremist groups, some of whom desire to foment civil war, were planning violence," said Bennie Thompson, chairman of the House Homeland Security Committee.
'Robust plan'
The images of hundreds of Trump supporters easily pushing into the main building of Congress despite a lockdown, striding through the halls and climbing on statues while guards had guns drawn to protect lawmakers, have never been seen before by Americans.
Police and defence officials said they had been planning for the January 6 rally of violent Proud Boys and other militia, QAnon conspiracy theorists, and other die-hard Trump followers for weeks.
It was timed for the day Congress was to confirm Joe Biden’s victory over Trump in the November 3 election -- a verdict Trump and followers have refused to accept.
Despite many planning meetings and tracking the likely attendees, officials said they didn't expect the group to besiege the Congress.
"The USCP had a robust plan established to address anticipated First Amendment activities," said Sund, referring to protests protected by the US constitution's guarantee of free speech.
Nobody called
The unique structure of policing in Washington, the US capital with broad swathes of federal government property but also a city unto itself, fed into the disastrous attack on Congress.
The Capitol Police control the area around the Congress, and the city's larger, better-trained force can't go there unless asked.
The siege of the Capitol building was well underway when they were called in at 1800 GMT on Wednesday, said metropolitan Washington police chief Robert Contee.
"Things were already pretty bad at that point," he told a press conference on Thursday.
The city government also directs local National Guard forces which had been called up to help with the demonstrations.
But Mayor Muriel Bowser said she was never asked for their help on Wednesday.
"The Capitol Police and the leadership at the Capitol, they did not make the decision to call in guard support. I cannot order the army, National Guard to the United States Capitol grounds."
In fact, said Army Secretary Ryan McCarthy, through multiple meetings with all the stakeholders including Capitol Police, Sund's team repeatedly rejected offers of provisional support.