hammer home vs reinforce

hammer home

verb
  • To repeatedly or continually emphasise (an opinion or idea) until or so that a person or group of people understands it. 

reinforce

verb
  • To encourage (a behavior or idea) through repeated stimulus. 

  • To strengthen, especially by addition or augmentation. 

  • To emphasize or review. 

How often have the words hammer home and reinforce occurred in a corpus of books? (source: Google Ngram Viewer )