I would say that the bigger racket is the democratic and republican party. If it were not for these two divergent ideological parties, the Congress might even function.
The source of the congressional racket begins with these parties, and their 3rd party contributors and supporters. They finance their election campaigns on a quid pro quo basis. So when these elected congress people are in power, they work for them, and not the people. That is the racket, as the people only cast the vote, but the strings that control congress are made during the election campaign.
The loyal party member is the mark, and they allow the party to pull their strings, and in turn the 3rd party pulls the strings and runs congress.
It is like putting your kids on the school bus, once in the bus you no longer control your kids. The school then controls your kids, and the school board controls how your kids are controlled.
3rd Party wealthy contributor -> Congress -> political party -> Loyal party voter
The only one in this sequence that doesn't get quid pro quo is the Loyal Party Voter.