In the history of the United States, "waving the bloody shirt" refers to the practice of politicians referencing the blood of martyrs or heroes to criticize opponents. In American history, the phrase gained popularity with a fictitious incident in which Benjamin Franklin Butler of Massachusetts, when making a speech on the floor of the U.S. House of Representatives, allegedly held up a shirt stained with the blood of a carpetbagger whipped by the Ku Klux Klan.[1] (While Butler did give a speech condemning the Klan, he never waved anyone's bloody shirt.[2])
The idea may be traced back to Julius Caesar's funeral in 44 BC when Mark Antony showed the toga to the crowd during his funeral oration, a scene which appears in William Shakespeare's Julius Caesar, but the speech mostly occasioned bathos.
Southerners mocked Butler, using the fiction of his having "waved the bloody shirt" to dismiss KKK and other atrocities committed against freed slaves and Republicans.[3] It also inspired the Southern Red Shirts.
Waving the bloody shirt also has been used to define someone who brings up a past injustice or mistreatment in history to justify or cover up an injustice being committed in the present.