It's really not a secret. Nobody in congress has all the information and they all rely on their staff. A senator or representative comes and goes but the staff is usually the same for years. These guys are political junkies and they give information to their boss that will make him look good while supporting whichever side they are on. If the congressman lacks character and principles, such as Rockefeller, they will end up making mistakes by being on both sides of issues. That's why we had the Kerry flip-flops. He had to flip-flop because his core principles came into play versus his past positions aided by pressure from his donors, special interest groups and the desire to win the election.
What staffs are you talking about--the staffs of the individeual representatives or the Senate/House committtee staffs?