Why is he getting involved?

I hate to defend a chud Senator, but it kinda looks like the marine has his hand trapped in the door and Sheehy’s trying to get him loose before the cops do further harm. Really hard to say from the shakey camera angle. But it looks like the security goons were going to happily tear his arm straight off if someone hadn’t stepped in.

There is no reason for a civilian to help in this situation.

To help the cops? No. To help the marine? There absolutely was.