buy into vs get behind

buy into

verb
  • To believe; to accept a craze or fad as valid. 

  • To buy stocks or shares of (a business). 

get behind

verb
  • To come to believe something; to change one's mind into a new position. 

  • To support, to cheer on. 

  • To have a trip or any pleasurable experience with drugs. 

  • To appreciate, to enjoy. 

  • Used other than figuratively or idiomatically: see get, behind. 

How often have the words buy into and get behind occurred in a corpus of books? (source: Google Ngram Viewer )