7. Dan Rostenkowski
Serving for 36 years, from 1959 to 1995 as a United States Representative from Chicago, Dan Rostenkowski was once considered one of the most powerful legislators in Congress, especially in matters of taxation. However, his actions between 1991 and 1995 would see him lose that power and end up behind bars in what would come to be known as the Congressional Post Office scandal.
It all began when the United States Capitol Police opened an investigation into a single embezzlement charge against a single Congressional Post Office employee. The evidence pointed to more and more employees being involved in a conspiracy to launder Post Office money through stamps and postal vouchers, with House Ways and Means Committee chairman Dan Rostenkowski being heavily involved.