Police officers who fought back against Trump supporters at the US Capitol on 6 January have given evidence about the violence and hatred they experienced.
They were testifying at the first hearing of a Congressional committee set up to investigate the attack.
Capitol Police Officer Harry Dunn, who is black, said he was taunted with a racial epithet by the mob.
At least 535 rioters have been arrested so far, but prosecutors have only secured a few convictions.
The inquiry is being conducted almost entirely by Democrats, after most Republicans boycotted the committee.
However, two Republicans – Liz Cheney and Adam Kinzinger – have broken ranks to join the investigation.
“If those responsible are not held accountable… this will remain a cancer on our constitutional republic,” Ms Cheney said as the hearing began.
The select committee was formed after Republicans objected to an independent commission like the one that investigated the 11 September 2001 attacks.
The four officers described being beaten and assaulted by rioters who had come to disrupt the certification of President Joe Biden’s election victory.
Officer Dunn said he told several protesters that he had voted for Mr Biden.
“Does my vote not count? Am I nobody?” he told them, after they wrongly claimed that the election was fraudulent.
“That prompted a torrent of racial epithets,” he testified. “One woman in a pink Maga [Make America Great Again] shirt yelled, ‘You hear that, guys, this [expletive] voted for Joe Biden!”
“No one had ever – ever – called me a [expletive] while wearing the uniform of a Capitol Police officer.”
The officers also criticised Republicans who have downplayed the violence of 6 January.
Officer Michael Fanone slammed his fist on the desk as he accused them of a “disgraceful” violation of their oaths of office.
Mr Kinzinger, one of the only Republicans who voted to impeach Mr Trump for his role in the riot, appeared to hold back tears as he criticised his colleagues.
“We still don’t know exactly what happened. Why? Because many in my party have treated this as just another partisan fight. It’s toxic and it’s a disservice to the officers and their families.”