What is the source of the allusion in the sentence below?
The candidate's fixation on his opponent's failure to wear a flag pin on flag day seemed at times to border on McCarthyism.

 - British history
 - U.S. history
The source of the allusion McCarthyism is U.S. history.
In the 1950 s, U.S. senator Joseph McCarthy led a ruthless investigation of Americans whom he accused of being Communist sympathizers. Based on flimsy or nonexistent evidence, the accusations created a climate of suspicion and fear.
The allusion McCarthyism means aggressive questioning of a person's patriotism.