Just woke up here over in Australia and catching up on what has happened. Wasn't expecting this, just a drawn out counting of the votes.
I can kind of understand what the cops did. They were outnumbered and very likely outgunned as well, given who they were dealing with. Better to let the protesters vent while taking photos of them for later attest after they disperse than risk an all out firefight in the Capitol Buildings. Its much easier to say the cops should have been more aggressive when your life isn't on the line. This isn't a peaceful BLM protest but an armed and violent mob.
At least that is my guess of the decision that someone up the chain of command made.