Mexican American vs wetback

Mexican American

noun
  • Any person of Latin American descent in the United States. 

  • Used other than figuratively or idiomatically: see Mexican, American. 

wetback

noun
  • A Mexican or Central American who illegally enters the United States of America from its southern border. 

  • A person of the mestizo race; a mojado. 

How often have the words Mexican American and wetback occurred in a corpus of books? (source: Google Ngram Viewer )