The Washington Post has an article suggesting that most of the newly elected Republican members of Congress will catch Potomac fever within a short time. As one conservative public relations person says, "They run against Washington calling it a cesspool and discover that it's really a hot tub." There's no news in the article, but it does raise the question of whether living and working in the capital leads to corruptive cooptation.
I think the real problem is the opposite: members spend so much time raising money and going back home that they never get to know their colleagues as human beings and never develop the institutional loyalty that allows Congress to see the national interest regardless of their local and political interests. In other words, a small case of Potomac fever protects against much worse diseases.