We should ban politicians with criminal records that have some terrible record. If the politicians have a record of something minor that was years ago and it was just a dumb mistake they made as a kid then it should not be taken seriously. But if it is recent and serious than yes.
Congress is responsible for checks and balances of actions taken by the executive branch, i.E. The NSA scandal. However, with criminal records congressmen and women cannot obtain security clearances needed to gain access to all documentation, thus limiting their ability to effectively do their job of oversight. As the system works right now the executive entities with classified programs are left to police themselves, and unconstitutional practices are able to go unchecked.