Not just poorly secured. Video shows the Capitol police literally opening the doors for them... them being POed demonstrators, main stream media, known antifa members (some claiming to be there to document the event).
It was bizarre. Many strolled into the building relaxed like it was a tour. Quite the opposite of the billions in damage to businesses in cities we have seen all over the country going back to the last Spring with fireworks, lasers, people with clubs, shields... claimed by the media to be "peaceful demonstrations".