Senators limited to two terms for a total of 12 years of service.
Representatives limited to five terms for a total of 10 years of service.
The founding fathers did not intent on creating career politicians. The faults of that system were recognized when the president's post was limited to two terms in office. However, congressmen and women continue to be allowed to be re-elected indefinitely.
Continually competing for re-election means politicians spend more time lobbying then legislating. They become ineffective and can't make hard decisions as they will simply "do it next term." Lastly, it reduces their understanding of the needs of the people as they have a propensity to simply stay in politics rather than return to business and the "real world" of the people they represent.