Are The Old Bosses Still in Charge?

What is the setting for the cartoon?
This cartoon takes place in the Senate, which is part of the Legislative branch.(House of Representatives)
What entrance is open, and what entrance is closed?
The people's entrance is closed, while the monopolists door is wide open. This shows how the rich have more power and are more important than the workers.
Who do you think the large men at the back of the room represent?
I think the large men in the background  are special interest groups, the wealthy.
Why would the large men be in the room in the first place?
The reason the special interest groups are there is that they want to influence how the laws are written. They are looking after themselves.

"Americans see their leaders in Washington as overpaid agents of wealthy individuals and corporations who are largely disconnected from the concerns of average Americans."