front runner vs groundbreaker

front runner

noun
  • One who engages in front running. 

  • Any of the most likely winners in a contest, election, etc. 

groundbreaker

noun
  • First person to do, make or fight for something. A pioneer; a seminal person. 

How often have the words front runner and groundbreaker occurred in a corpus of books? (source: Google Ngram Viewer )