This was a shameful display by the police charged with defending the rule of law in the USA, and even more than protesters, the police who plainly allowed this to happen must be investigated and tried. Whether those are the boots on the ground or the higher ups I have no idea, but this can't be left to stand.
Given what we've seen tonight, this could have easily turned into a putsch attempt, and it would have been very hard to stop it once the mob was allowed inside the building. They could have taken senators and congressmen hostage, they could have forced them to overturn the elections in a mock session, they could have killed dissenters - it was only by luck that it turned out they were disorganized and essentially there for a stunt.