ballot box vs revolving door

ballot box

noun
  • The process or method of voting. 

  • A sealed box with a slit, into which a voter puts a completed voting slip. 

revolving door

noun
  • 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. 

  • A door that rotates around a central pivot. 

  • A system or institution in which people exit and immediately reenter. 

  • Synonym of recidivism 

How often have the words ballot box and revolving door occurred in a corpus of books? (source: Google Ngram Viewer )