That guy on the right, wearing the red baseball cap (and off the right shoulder of Ashli Babbitt) -- he seemed to function as some kind of observer.
That guy (red cap) is wearing a Don't Tread on Me flag. He is briefly seen, in the following video, starting at 0:12.
https://www.youtube.com/watch?v=ldqDgTlOfq4
By 0:15 in that video, three Capitol Police officers (two of whom, you see to your left in the above pic) have just been stepping aside (why?) from doors they were protecting, and the fellow (red cap) is at the same time, stepping toward the same doors they guarded.
Where said fellow (red cap) at 0:18 in the video, tests or confirms that the doors are not budging. After which, said fellow (red cap) does a quick about face and leaves the area.