I would say lawyers and bankers/financiers. Lawyers seem to lapse into case law discussions where the average common sense person's eyes would glaze over and would revert the discussion to where it needs to be - the Constitution. I think equally privileged and elitist are the bankers. If I were president, I'd certainly want to break up this lovefest amongst Goldman Sachs, the government, and the Fed. I was struck when Michelle Bachman asked Tim Geithner to tell her where in the Constitution it said he had the right to do (whatever it was he was doing). He acted as if he had never heard of the document. Scary.
What I am speaking of, and what Madison was talking about as well, is any group with similar interests gaining control of all three branches of government.
Look closely at all three branches of our government today and see what group you think that might be.