get after vs impugn

get after

verb
  • To attempt to convince another to move into action. 

  • To move into action in pursuit of something. 

  • To move into action in attempt to catch or defeat another. 

impugn

verb
  • To verbally assault, especially to argue against an opinion, motive, or action; to question the truth or validity of. 

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