I feel people are looking at the lack of security the wrong way. It could be a gambit played by bother sides. On the one hand, the Democrats love it because it allows them to show violence and then suggest tighter security and change in laws to make the country "safer". For the Republicans/Trump, less security means they could of has a person infiltrate the building or even one of the security people was working with them to obtain information such as Nancy Pelosi's laptop.

Basically, the protest going into the Capitol needed to be done to hide any breaking an entering. The Breaking and entering potentially already occurred before the people even went inside the building. This would explain why they are so desperate to impeach him even though his term is supposedly almost up. They are scared of what he may of confiscated from the Capitol building.

Granted, I think if one is using government property, such as a laptop, the President should be able to view it whenever they want to make sure the person in question is doing their job.