lean on vs rule with a rod of iron

lean on

verb
  • To put pressure on; to attempt to compel a person to do something; to exert influence on. 

  • Used other than figuratively or idiomatically: see lean, on. 

  • To depend upon for support; to require assistance from. 

  • To criticize or reprimand for the purpose of changing behavior. 

rule with a rod of iron

verb
  • To rule with stern severity. 

How often have the words lean on and rule with a rod of iron occurred in a corpus of books? (source: Google Ngram Viewer )