Johnny-One-Note Meaning

(idiomatic, chiefly US, Canada) An opinion or viewpoint on a single subject or a few particular subjects which is frequently expressed by a person or organization.

Example: 1945 July 9, “The Press: Confessions of a Grouch”[1], Time, volume 46, number 1:
  Whether his boss (Hearst) had told him to get off his Johnny-one-note of hate toward labor leaders, foreigners and New Dealers, or whether Pegler had decided all by himself to change his tune, no one knew.