They have a carpet change halfway through the plane. Forward of the plane the carpet is one color and considered “White House.” Aft is another color and is for press and riding dignitaries. Secret Service is there to enforce it.

The rule is you can go aft of your assigned seat but you are not allowed to go forward of your assigned seat.

I am an AF1 fag. I learned this by my consumption of YT videos with interviews of the air crew in the Presidential Airlift Group. That’s all. :)