The U.S. Capitol Police answer to Congress. Mitch McConnell was Senate leader, and Nancy Pelosi was speaker of the House. Therefore, they were in control of the Capitol Police. They made little effort to prepare for Trumps rally, which everyone knew ahead of time would be massive. They had one or two lines of flimsy barricades that were undermanned. Once Trumps supporters marched on the Capitol building, they easily overran security and made their way inside. The Capitol Police were deliberately set up to fail by Pelosi and McConnel.

They did this knowing that it would lead to a chaotic situation that could be used as a pre-text to shove the electoral votes through, and sweep aside all objections over their validity. When the protesters made their way inside the Capitol building, members of Congress were hastily evacuated. When they reconvened later that day, they counted the electoral votes for Biden (even from contested states) and gave him the Presidency.

Meanwhile, the media had a field day with the protests at the Capitol, and used it as an opportunity to demonise Trump and his supporters. They grossly exaggerated the violence of the protesters (which was particularly glaring in the face of how they excused the rioters during the summer of 2020), and even labelled it an act of 'domestic terrorism.' Congress tried to impeach Trump even though he was already on his way out. But McConnell and the GOP backed down once they realised that Trumps supporters would abandon them if they pushed forward on impeachment.