revolving door

Short definition from Wiktionary

Noun

1. 1
   A door that rotates around a central pivot.
2. 2
   A system or institution that people exit and immediately reenter.
3. 3
   A movement of personnel between roles as legislators and regulators, on the one hand, and members of the industries affected by the legislation and regulation, on the other.
4. 4
   Synonym of recidivism.