The left middle guy makes a statement, and as he finishes, the back row guy stands up and proclaims assent. The front row guy then stands up and starts agreeing and the right middle row guy chines in. It makes the room think everyone else agrees with the point.
Great control tactic.
If the Rats had any sense, they would have had at least a small audience and overplayed a laugh track on that routine.
“If the Rats had any sense...”
...they wouldn’t be Democrats.